This research was supported by an NSF Graduate Research Fellowship to Danielle R. Perszyk and a NIH grant to Sandra R. Waxman (R01HD083310).

The following procedures were approved by the Northwestern University Institutional Review Board and informed consent was obtained from the caregivers of all infants. We recruited infants being raised in environments with more than 50% exposure to English11,17. Infants in all experiments first listened to a soundtrack in which we manipulated their exposure to either lemur vocalizations or backward speech; they then participated in an object categorization task. What varied across infants was (a) the kind of signal they heard in the exposure manipulation and the categorization task (either lemur vocalizations or backward speech) and (b) the extent of the exposure phase (either brief exposure in the lab or prolonged exposure at home). For all infants, the categorization task took place in the lab.
1. Materials
<ol>
	<li>How to create the exposure manipulations
	<ol>
		<li>Select 8 distinct samples of lemur vocalizations and 8 distinct samples of backward speech, each 2 to 4 s in duration. Together, the 8 samples should yield 30 s of each acoustic signal. Ensure that the lemur and backward speech segments are matched as closely as possible for duration (e.g., ~3 s in duration) and for mean frequency (e.g., ~300 Hz).
		<ol>
			<li>To obtain lemur vocalizations, search a database of animal vocalizations or contact a researcher who collects animal vocalizations.</li>
			<li>To create backward speech segments, use a laptop and a software program (e.g., Audacity) to (1) record a research assistant speaking ~3 s sentences in infant-directed speech and (2) temporally reverse (in Audacity: Effect &#62; Reverse) each speech segment.</li>
		</ol>
		</li>
		<li>Choose a piece of classical instrumental music that is longer than 4 min. Here, we used the first 4 min of Beethoven&#39;s String Quartet in C Minor, Op 18 No. 4: III. Menuetto.</li>
		<li>Use an audio editing software program (e.g., Audacity) to import the music (in Audacity: File &#62; Import) and select a portion of the piece that is approximately 4 min in duration (highlight and delete the remainder of the piece).
		<ol>
			<li>Create 2 distinct soundtracks by inserting (i.e., copying and pasting) the 8 selected segments of each type (lemur vocalizations or backward speech) into the musical soundtrack.</li>
			<li>To create the &#34;Lemur&#34; soundtrack, open the 8 lemur vocalization sound files in the same software program (e.g., Audacity) and insert them into the file with the music.
			<ol>
				<li>To do so, highlight an entire lemur vocalization, navigate to Edit &#62; Copy, place the cursor in the music file, and navigate to Edit &#62; Paste. Insert the vocalizations at irregular intervals throughout the soundtrack. Do not place them at musical phrase boundaries. Do this twice for each lemur vocalization, inserting them in a pseudorandomized order to ensure that no 2 identical vocalizations occur in a row. Together, this yields a 5 min loop (4 min of music, interspersed with 1 min of lemur vocalizations).</li>
				<li>Repeat this 5 min soundtrack so that the entire soundtrack lasts approximately 10 min. To do so, highlight the entire 5 min section, navigate to Edit &#62; Copy, place the cursor at the end of the 5-min section, and navigate to Edit &#62; Paste.</li>
			</ol>
			</li>
			<li>To create the 10 min &#34;Backward Speech&#34; soundtrack, replace each lemur vocalization in the Lemur soundtrack with a selected segment of backward speech, using the same pseudorandomized order.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>How to create the categorization task
	<ol>
		<li>Visual materials: Create 2 sets of line drawings by hand. In each set, include 9 members of the same object category (here, use 9 distinct drawings of dinosaurs and 9 distinct drawings of fish). Use a different bright color for each drawing within a given category. Scan these drawings onto a computer and save them as image files. Note that the drawings should be unfamiliar objects to infants at the ages tested.</li>
		<li>Acoustic materials: Select one lemur vocalization and one backward speech segment that were not included in either of the exposure manipulations (1.1.3). Match the lemur and backward speech segments as closely as possible for duration (e.g., ~3 s in duration) and for mean frequency (e.g., ~300 Hz).</li>
		<li>Program a task in MATLAB that includes a familiarization phase and a test phase; this task will be projected onto a 5 ft by 5 ft screen in front of the infant.
		<ol>
			<li>Program the familiarization phase such that 8 of the visual exemplars from a single category (e.g., 8 dinosaurs, each a different color) appear sequentially. Each exemplar should appear for 20 s, on either the right or left side of a screen, in alternating fashion. Create 2 distinct versions, pairing each familiarization exemplar with one of the acoustic stimuli below (&#34;Lemur&#34; and &#34;Backward Speech&#34; conditions, respectively). In both conditions, the acoustic stimulus should occur twice on each familiarization trial; once when the visual exemplar appears, and once again 10 s later.
			<ol>
				<li>In the Lemur condition, program each familiarization exemplar to appear simultaneously with a lemur vocalization.</li>
				<li>In the Backward Speech condition, program each familiarization exemplar to appear simultaneously with a backward speech segment.</li>
			</ol>
			</li>
			<li>During the test phase, present the 9th exemplar from the familiar category (e.g., another dinosaur) and an exemplar from the other category (e.g., a fish). These two images should be identical in color and presented simultaneously (one presented on the right and the other on the left side of the screen) in silence for 20 s.</li>
		</ol>
		</li>
		<li>In programming the categorization task, counterbalance (1) which category will be presented during the familiarization phase, (2) the side on which the first familiarization image will appear, and (3) the side on which the novel and familiar test images will appear.</li>
	</ol>
	</li>
</ol>
2. General Procedures
<ol>
	<li>Exposure phase
	<ol>
		<li>Place the infant close to the caregiver or on their lap in a quiet area. Place a laptop or tablet within the infant&#39;s viewing range (from 1 to 4 ft from the infant).</li>
		<li>Use the laptop or tablet to present either the Lemur or the Backward Speech soundtrack.</li>
	</ol>
	</li>
	<li>Categorization task
	<ol>
		<li>In a semi-darkened test room in the lab, seat the caregiver on a chair 4 ft from a 5 ft by 5 ft screen. Connect the laptop with the categorization task programmed in MATLAB to (1) the screen that will display the categorization task and (2) a projector that will project the task onto the screen.</li>
		<li>Seat the infant on the caregiver&#39;s lap, facing forward.</li>
		<li>Instruct the caregiver to avoid influencing the infant&#39;s behavior in any way. More specifically, instruct them to remain quiet and still throughout the duration of the task and to keep their infant centered, using their midline as a guide. Provide caregivers with a pair of blacked-out glasses to ensure that they cannot see the visual materials.</li>
		<li>Turn on the projector.</li>
		<li>Turn on recording equipment to capture the infants&#39; behavior throughout the task.</li>
		<li>Begin the categorization task by pressing &#34;Run&#34; in MATLAB: Present the Lemur condition if the infant was exposed to the Lemur soundtrack and the Backward Speech condition if the infant was exposed to the Backward Speech soundtrack.</li>
	</ol>
	</li>
	<li>Coding (categorization task only)
	<ol>
		<li>Code the onset and offset of each infant&#39;s left and right looks during both the familiarization and test phases.</li>
		<li>Exclude infants who (1) look at fewer than 6 of the familiarization exemplars; (2) look during less than 40% of the familiarization phase. Also exclude infants if there is parental interference, experimental error or technical failure, or if their performance at test is greater than 2 SD from the mean.</li>
	</ol>
	</li>
	<li>Analyses
	<ol>
		<li>For the familiarization phase, calculate the total the amount of time each infant looked at the familiarization objects.</li>
		<li>For the test phase, calculate a preference score for each infant: (total looking time to novel test image)/(total looking time to both test images).</li>
	</ol>
	</li>
</ol>
3. Experiment 1: Brief Exposure to Lemur Vocalizations
<ol>
	<li>Participants
	<ol>
		<li>Recruit 14 infants at 6 to 7 months of age.</li>
	</ol>
	</li>
	<li>Procedure
	<ol>
		<li>Invite the caregiver and infant into a quiet, comfortable room. In our lab, this room is adjacent to the testing room.</li>
		<li>Exposure manipulation: Play the Lemur soundtrack once, with the music visualizer (e.g., iTunes) present on the screen.</li>
		<li>Categorization task: When the soundtrack finishes, guide the caregiver and infant into the testing room. Begin the categorization task (Lemur condition).</li>
	</ol>
	</li>
</ol>
4. Experiment 2: Brief Exposure to Backward Speech
<ol>
	<li>Participants
	<ol>
		<li>Identical to Experiment 1.</li>
	</ol>
	</li>
	<li>Procedure
	<ol>
		<li>Invite the caregiver and infant into a quiet, comfortable room.</li>
		<li>Exposure manipulation: Play the Backward Speech soundtrack once, with the music visualizer present on the screen.</li>
		<li>Categorization task: When the soundtrack finishes, guide the caregiver and infant into the testing room. Begin the categorization task (Backward Speech condition).</li>
	</ol>
	</li>
</ol>
5. Experiment 3: Prolonged Exposure to Lemur Vocalizations
<ol>
	<li>Participants
	<ol>
		<li>Recruit 14 infants at 4.5 months of age.</li>
	</ol>
	</li>
	<li>Procedure
	<ol>
		<li>By phone, invite the caregiver to participate in a 6 week long study. Explain that the study requires them to expose their infant, at home, to a 10 min soundtrack that contains 8 min of music and 2 min of lemur vocalizations (i.e., Lemur soundtrack). Explain that the study lasts for 6 weeks, beginning when the infant is 4.5 months and ending when the infant is 6 months of age.</li>
		<li>Provide caregivers with this precise tapering schedule7,8,18
		<ol>
			<li>Week 1: Play the soundtrack to infant once a day, every day.</li>
			<li>Week 2: Play the soundtrack to infant once every other day.</li>
			<li>Week 3: Play the soundtrack to infant 3 times during the week.</li>
			<li>Weeks 4-6: Play the soundtrack to infant 2 times per week.</li>
		</ol>
		</li>
		<li>To ensure the fidelity of the exposure manipulation throughout the 6 week exposure manipulation, share with caregivers an online interactive document that (a) outlines their role at every step throughout the 6 week period and (b) asks them to record each date and time at which they played the soundtrack to their infant.</li>
		<li>Send weekly reminders by phone or email to keep caregivers engaged and on track.</li>
		<li>During Week 5, schedule a lab visit for the following week (Week 6). Instruct caregivers that infants should listen to the soundtrack 2 to 4 days before their scheduled lab visit; infants should not listen to the soundtrack either on the day of or the day preceding their visit. 
		NOTE: At the lab visit, there is no exposure manipulation: Infants participate only in the categorization task from Experiment 1 (Lemur condition).</li>
	</ol>
	</li>
</ol>

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<li>Vouloumanos, A., Hauser, M. D., Werker, J. F., Martin, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+tuning+of+human+neonates%27+preference+for+speech%5BTitle%5D)+AND+%22Child+dev%22%5BJournal%5D)">The tuning of human neonates' preference for speech.</a> Child dev. 81 (2), 517-527 (2010).</li>
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<li>Lewkowicz, D. J., Ghazanfar, A. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+emergence+of+multisensory+systems+through+perceptual+narrowing%5BTitle%5D)+AND+%22Trends+cogn+sci%22%5BJournal%5D)">The emergence of multisensory systems through perceptual narrowing.</a> Trends cogn sci. 13 (11), 470-478 (2009).</li>
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<li>Friendly, R. H., Rendall, D., Trainor, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Plasticity+after+perceptual+narrowing+for+voice+perception%3A+reinstating+the+ability+to+discriminate+monkeys+by+their+voices+at+12+months+of+age%5BTitle%5D)+AND+%22Frontiers+in+psychology%22%5BJournal%5D)">Plasticity after perceptual narrowing for voice perception: reinstating the ability to discriminate monkeys by their voices at 12 months of age.</a> Frontiers in psychology. 4, October 718(2013).</li>
<li>Pascalis, O., Scott, L. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Plasticity+of+face+processing+in+infancy%5BTitle%5D)+AND+%22Proc+Natl+Acad+Sci+USA%22%5BJournal%5D)">Plasticity of face processing in infancy.</a> Proc Natl Acad Sci USA. 102 (14), 5297-5300 (2005).</li>
<li>Heron-Delaney, M., Anzures, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Perceptual+training+prevents+the+emergence+of+the+other+race+effect+during+infancy%5BTitle%5D)+AND+%22PloS+one%22%5BJournal%5D)">Perceptual training prevents the emergence of the other race effect during infancy.</a> PloS one. 6 (5), 19858(2011).</li>
<li>Brown, R. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aBrown%2C+R+%22Words+and+things%3A+An+introduction+to+language%22">Words and things: An introduction to language</a>. , The Free Press. Glencoe, IL. (1958).</li>
<li>Fulkerson, A. L., Waxman, S. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Words+%28but+not+tones%29+facilitate+object+categorization%3A+Evidence+from+6-+and+12-month-olds%5BTitle%5D)+AND+%22Cognition%22%5BJournal%5D)">Words (but not tones) facilitate object categorization: Evidence from 6- and 12-month-olds.</a> Cognition. 105 (1), 218-228 (2007).</li>
<li>Ferry, A. L., Hespos, S. J., Waxman, S. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Categorization+in+3-+and+4-month-old+infants%3A+An+advantage+of+words+over+tones%5BTitle%5D)+AND+%22Child+dev%22%5BJournal%5D)">Categorization in 3- and 4-month-old infants: An advantage of words over tones.</a> Child dev. 81 (2), 472-479 (2010).</li>
<li>Balaban, M. T., Waxman, S. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Do+words+facilitate+object+categorization+in+9-month-old+infants%5BTitle%5D)+AND+%22J+exp+child+psychol%22%5BJournal%5D)">Do words facilitate object categorization in 9-month-old infants.</a> J exp child psychol. 64, 3-26 (1997).</li>
<li>Mareschal, D., Quinn, P. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Categorization+in+infancy%5BTitle%5D)+AND+%22Trends+Cogn+Sci%22%5BJournal%5D)">Categorization in infancy.</a> Trends Cogn Sci. 5 (10), 443-450 (2001).</li>
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The authors have nothing to disclose.

Here we outline a procedure for examining the role of experience in linking sounds and core cognitive processes early in infancy. Our combined experiments document the first evidence that experience plays a central role in guiding infants to specify which signals, from a broad initial set of possibilities, they will harness to core conceptual processes that ultimately provide the foundations of meaning. They also reveal an intricate interface between nature and nurture: Although experience plays little role, if any, in determining the broad set of signals that infants initially link to cognition17, experience is vital in guiding infants to tune out irrelevant signals from the initially privileged set and, instead, tune into the those they will continue to link to meaning.
Our exposure procedure has demonstrated that at 6 and 7 months, when the link between lemur vocalizations and object categorization would otherwise have been severed17, merely exposing infants to this signal has a dramatic effect. As has similarly been observed in the perceptual narrowing literature5,6,7,8, this exposure procedure demonstrated infants&#39; plasticity, permitting them either to reinstate or maintain a developmentally prior link (Experiments 1, 3). It has also identified principled limits on the kinds of signals that exposure alone may act on. For signals not included in infants&#39; initial endowment (e.g., backward speech), experience alone appears to be insufficient for creating, de novo, a link to cognition (Experiment 2).
Three aspects of our protocol are essential for interpreting the effects of exposure on infants&#39; acquisition of an increasingly precise link between acoustic signals and cognition. First, during the exposure manipulation, the signals must be embedded within a non-social context (we chose classical music) to engage infants&#39; attention without introducing social or communicative cues. Second, the exposure manipulation must include several different samples of the acoustic signal (we used 8); such variation helps keep infants engaged in the listening task. Third, the sound presented during the categorization task must not be one that infants heard earlier in the exposure manipulation.
Importantly, our exposure manipulation also opens several new avenues for future work. Are there critical periods for tuning the link between privileged signals and cognition? Which other cognitive capacities, if any, are supported by these signals? And what does it mean to be a &#34;privileged signal?&#34; The current results represent an important first step in identifying how exposure to certain ambient signals guides infants to identify which of those signals will ultimately carry meaning; further studies will help paint a more nuanced picture of the delicately balanced, cascading interactions between infants&#39; inborn capacities and their environments, which collectively scaffold the foundation for their acquisition of language.

Human infants are born ready to acquire language, a cultural and cognitive tool that defines us as a species and fundamentally shapes our development. Central to our capacity for learning language are two unique features of human development: Our altriciality and our powerful learning strategies. Together, these features unlock a remarkable degree of early plasticity that enables infants to be highly attuned to input from their environments. For example, although infants come into the world with a set of perceptual preferences and discriminatory capacities sufficiently broad to include the faces and voices of human and nonhuman primates, within months they narrow these preferences to exclusively human signals1,2,3. This process of perceptual narrowing is adaptive on two counts: It increases the signal-to-noise ratio of relevant communicative signals &#8212; those that will guide infants to efficiently and accurately navigate their complex social world &#8212; and it paves the way for integrating information across perceptual modalities (e.g., integrating faces and voices)4 &#8212; an essential element for the multimodal nature of human language. Moreover, because of infants&#39; early plasticity, perceptual narrowing can be prevented or reversed with exposure to nonnative signals (e.g., nonnative language, nonhuman faces, foreign musical rhythms)5,6,8. This illustrates that perceptual narrowing is experience-driven.
Yet to master their native language, infants must do more than tune in to the faces and voices of its speakers. The power of human language is inextricably linked to cognition9. Incredibly, even in their first year of life, infants have begun to link language and cognition: Simply listening to human language promotes infants&#39; ability to form object categories, a building block for their cognition10,11,12.
This is not to say that infants can only form object categories if they are listening to language. On the contrary, decades of research reveal that infants in their first months of life can form at least some object categories in the absence of any sounds13. But not all object categories are equally easy for infants to form. The slightly more difficult categories provide a powerful opportunity to uncover what effect, if any, language may have on infant categorization. To do so, researchers identify object categories that are more difficult for infants to discern in the absence of other supporting information (like language) and then ask whether language (and other sounds) offer infants any advantage in categorization.
Using this logic, an early link between language and object categorization was documented in a novelty preference paradigm designed to accommodate very young infants (Figure 1b)11. This paradigm has two phases. During the familiarization phase, all infants view images of a series of distinct objects (e.g., dinosaurs) presented sequentially in conjunction with a sound. During the test phase, all infants view two new images in silence: One is a new member of the now-familiar category (e.g., another dinosaur) and the other is a member of a novel category (e.g., a fish). Infants&#39; looking time at test serves as an index of categorization. If infants form the category during familiarization, then at test they should distinguish the novel from the familiar image. If infants fail to do so, then at test they should perform at chance14,15,16.
The results were striking. At 3, 4, and 6 months, infants listening to language during familiarization &#8212; but not tone sequences &#8212; successfully formed object categories11,17. Surprisingly, language is not the only sound that exerts this cognitive advantage: At 3 and 4 months, listening to vocalizations of nonhuman primates (Madagascar, blue-eyed lemur: Eulemur macaco flavifrons) confers the same cognitive advantage as human vocalizations17. By 6 months of age, however, infants have tuned this initially broad link specifically to human vocalizations; lemur vocalizations no longer exert an advantageous effect on infant categorization17.
But what mechanism underlies infants&#39; increasing precision in linking language and cognition? Here, we consider the contribution of infants&#39; experience. Does infants&#39; rich experience with human language (and their dearth of experience listening to lemur vocalizations) play a role as they narrow the link between initially privileged signals (e.g., human and nonhuman primate vocalizations) and the core cognitive process of object categorization? Certainly, we cannot test this by manipulating infants&#39; exposure to language. But we can manipulate their exposure to lemur vocalizations. We focus on infants at 6 and 7 months of age &#8212; infants who, in the absence of exposure, no longer link lemur vocalizations and object categorization17. In Experiment 1, we ask whether brief exposure to lemur vocalizations permits them to preserve the link between this signal and object categorization. In Experiment 2, we ask whether brief exposure to backward speech &#8212; a signal that consistently fails to support object categorization at any age17 &#8212; also promotes object categorization. In Experiment 3, we put the question of exposure to a more stringent test, examining whether more prolonged exposure to lemur vocalizations permits them to preserve their initially-broad link.

<table><tbody><tr><td>Laptop 1</td><td></td><td></td><td>Use for presenting exposure soundtrack; preferably using iTunes Visualizer</td></tr><tr><td>Laptop 2</td><td></td><td></td><td>Use for programming and presenting categorization task</td></tr><tr><td>Laptop 3 (optional)</td><td></td><td></td><td>Use for coding infant looking behavior (can also use one of the above laptops)</td></tr><tr><td>Coding software</td><td>SuperCoder</td><td></td><td>Use for coding infant looking behavior</td></tr><tr><td>Video recorder</td><td></td><td></td><td>Use for recording infants&#039; face (looking behavior during categorization task)</td></tr><tr><td>Mixer</td><td></td><td></td><td>Use for integrating information from the video recorder (infant looking behavior) and the visual stimuli (categorization task)&amp;nbsp;</td></tr><tr><td>DVD player</td><td></td><td></td><td>Use for recording the input from the video recorder (infant looking behavior)</td></tr><tr><td>Television</td><td></td><td></td><td>Use for viewing input from mixer (screen-in-screen; categorization task in corner of screen showing infant looking behavior)&amp;nbsp;</td></tr><tr><td>Projector</td><td></td><td></td><td>Use for projecting visual stimuli of categorization task on screen</td></tr><tr><td>Speakers</td><td></td><td></td><td>Use for presenting auditory stimuli during categorization task</td></tr><tr><td>Blacked-out sunglasses</td><td></td><td></td><td>Use for blocking caretaker&#039;s vision during categorization task</td></tr><tr><td>Statistical analysis software</td><td>R</td><td></td><td>Use for analyzing infant looking behavior</td></tr></tbody></table>

experience is instrumental in tuning a link between language and cognition: evidence from 6-  to 7- month-old infants' object categorization

At birth, infants not only prefer listening to human vocalizations, but also have begun to link these vocalizations to cognition: For infants as young as three months of age, listening to human language supports object categorization, a core cognitive capacity. This precocious link is initially broad: At 3 and 4 months, vocalizations of both humans and nonhuman primates support categorization. But by 6 months, infants have narrowed the link: Only human vocalizations support object categorization. Here we ask what guides infants as they tune their initially broad link to a more precise one, engaged only by the vocalizations of our species. Across three studies, we use a novel exposure paradigm to examine the effects of experience. We document that merely exposing infants to nonhuman primate vocalizations enables infants to preserve the early-established link between this signal and categorization. In contrast, exposing infants to backward speech &#8212; a signal that fails to support categorization at any age &#8212; offers no such advantage. Our findings reveal the power of early experience as infants specify which signals, from an initially broad set, they will continue to link to cognition.

Using the procedures outlined above (Figure 1), we ran three experiments to test the effects of exposure as infants refine the links between certain sounds and cognition.
Results of Experiment 1 revealed that brief exposure to lemur vocalizations had a striking effect. Seven month-olds exposed to lemur vocalizations reliably preferred the novel test image, M = 0.57, SD = 0.09; t(13) = 3.12, p = 0.008, d = 1.73 (Figure 2). Their success in forming object categories diverges with infants&#39; failure to do so without exposure, at an age after which they had tuned out lemur vocalizations17. In contrast, results of Experiment 2 revealed that brief exposure to backward speech had no effect. Seven-month-olds exposed to backward speech performed at chance, M = 0.47, SD = 0.11; t(13) = -0.98, p = 0.34, d = 0.54 (Figure 2). Their chance performance mirrors that of infants who receive no exposure17. Importantly, infants&#39; successful categorization in Experiment 1 and failure in Experiment 2 cannot be a consequence of differences in their visual engagement with the two signals: Between the two experiments, there were no differences in infants&#39; mean accumulated looking times during familiarization, t(26) = 1.5, p = 0.14.
Together, results from Experiments 1 and 2 demonstrate that merely exposing infants to signals that were once part of infants&#39; initially broad template &#8212; but not signals that were not &#8212; enables infants to reinstate a link between these signals and cognition. Next, we tested the robustness of the effects of exposure to an initially privileged signal.
Results of Experiment 3 revealed that prolonged exposure to lemur vocalizations had the same effect as in Experiment 1. Six month-olds, who had not heard a lemur vocalization for days (M = 2 days, SD = 2 days), nonetheless successfully formed object categories, M = 0.59, SD = 0.14, t(13) = 2.52, p = 0.026, d = 1.4 (Figure 2). Their successful categorization paralleled that of infants who had heard lemur vocalizations moments before the categorization task (Experiment 1), t(22.1) = 0.44, p = 0.66.
<img alt="Figure 1" src="/files/ftp_upload/55435/55435fig1.jpg" /> 
Figure 1: Experimental design. In the Exposure Phase (A), infants listened to either 2 min of lemur vocalizations (Experiments 1 and 3) or 2 min of backward speech segments (Experiment 2), embedded within a 10 min soundtrack of classical music. After exposure, infants participated in the Categorization Task (B) from Ferry et al., 2013. During familiarization, each infant viewed 8 distinct visual images (20 s each) from the same category, presented sequentially, in conjunction with either a lemur vocalization (Experiments 1 and 3) or a backward speech segment (Experiment 2). Signals presented during exposure differed from those presented in the Categorization Task; in the latter, the same signal (either a lemur call or a backward speech segment) was presented twice during each familiarization trial. At test (20 s), infants viewed 2 images &#8212; a new member of the now-familiar category and a member of a novel category &#8212; presented simultaneously in silence. <a href="http://cloudflare.jove.com/files/ftp_upload/55435/55435fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/55435/55435fig2.jpg" /> 
Figure 2: Infants&#39; Preference Scores at test across experiments. Infants exposed to lemur vocalizations (Experiments 1 and 3) reliably preferred the novel test image, indicating that they had formed the object category. In contrast, infants exposed to backward speech (Experiment 2) performed at chance. Error bars represent &#177;1 SEM. Significant differences between Preference Score and chance performance (0.50) and between test conditions are marked by a single asterisk (p &#60; 0.05) or double asterisk (p &#60; 0.01). <a href="http://cloudflare.jove.com/files/ftp_upload/55435/55435fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Experience is Instrumental in Tuning a Link Between Language and Cognition: Evidence from 6-  to 7- Month-Old Infants' Object Categorization at JoVE.com

Experience is Instrumental in Tuning a Link Between Language and Cognition: Evidence from 6-  to 7- Month-Old Infants' Object Categorization

At 3-4 months, listening to human and nonhuman primate vocalizations boosts infants&#39; cognition; by 6 months, only human vocalizations exert this cognitive advantage. We describe an exposure manipulation that reveals the powerful shaping role of experience as infants specify which sounds to link to cognition and which to tune out.

At birth, infants not only prefer listening to human vocalizations, but also have begun to link these vocalizations to cognition: For infants as young as ...

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Thinking, Language And Intelligence

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6.6K Views.  Northwestern University. At 3-4 months, listening to human and nonhuman primate vocalizations boosts infants' cognition; by 6 months, only human vocalizations exert this cognitive advantage. We describe an exposure manipulation that reveals the powerful shaping role of experience as infants specify which sounds to link to cognition and which to tune out.

Video: Experience is Instrumental in Tuning a Link Between Language and Cognition: Evidence from 6-  to 7- Month-Old Infants' Object Categorization

Infant Auditory Processing and Event-related Brain Oscillations

Rapid auditory processing and acoustic change detection abilities play a critical role in allowing human infants to efficiently process the fine spectral and temporal changes that are characteristic of human language. These abilities lay the foundation for effective language acquisition; allowing infants to hone in on the sounds of their native language. Invasive procedures in animals and scalp-recorded potentials from human adults suggest that simultaneous, rhythmic activity (oscillations) between and within brain regions are fundamental to sensory development; determining the resolution with which incoming stimuli are parsed. At this time, little is known about oscillatory dynamics in human infant development. However, animal neurophysiology and adult EEG data provide the basis for a strong hypothesis that rapid auditory processing in infants is mediated by oscillatory synchrony in discrete frequency bands. In order to investigate this, 128-channel, high-density EEG responses of 4-month old infants to frequency change in tone pairs, presented in two rate conditions (Rapid: 70 msec ISI and Control: 300 msec ISI) were examined. To determine the frequency band and magnitude of activity, auditory evoked response averages were first co-registered with age-appropriate brain templates. Next, the principal components of the response were identified and localized using a two-dipole model of brain activity. Single-trial analysis of oscillatory power showed a robust index of frequency change processing in bursts of Theta band (3 - 8 Hz) activity in both right and left auditory cortices, with left activation more prominent in the Rapid condition. These methods have produced data that are not only some of the first reported evoked oscillations analyses in infants, but are also, importantly, the product of a well-established method of recording and analyzing clean, meticulously collected, infant EEG and ERPs. In this article, we describe our method for infant EEG net application, recording, dynamic brain response analysis, and representative results.

High-density electroencephalography (dEEG) is being used increasingly to study brain development and plasticity in the early years of life. Here we present an application of sophisticated analysis techniques that builds on traditional EEG recording to understand the oscillatory dynamics of rapid auditory processing in the infant brain.

Rapid auditory processing and acoustic change detection abilities play a critical role in allowing human infants to efficiently process the fine spectral ...

Examining Recall Memory in Infancy and Early Childhood Using the Elicited Imitation Paradigm

The ability to recall the past allows us to report on details of previous experiences, from the everyday to the significant. Because recall memory is commonly assessed using verbal report paradigms in adults, studying the development of this ability in preverbal infants and children proved challenging. Over the past 30 years, researchers have developed a non-verbal means of assessing recall memory known as the elicited or deferred imitation paradigm. In one variant of the procedure, participants are presented with novel three-dimensional stimuli for a brief baseline period before a researcher demonstrates a series of actions that culminate in an end- or goal-state. The participant is allowed to imitate the demonstrated actions immediately, after a delay, or both. Recall performance is then compared to baseline or to performance on novel control sequences presented at the same session; memory can be assessed for the individual target actions and the order in which they were completed. This procedure is an accepted analogue to the verbal report techniques used with adults, and it has served to establish a solid foundation of the nature of recall memory in infancy and early childhood. In addition, the elicited or deferred imitation procedure has been modified and adapted to answer questions relevant to other aspects of cognitive functioning. The broad utility and application of imitation paradigms is discussed, along with limitations of the approach and directions for future research.

The elicited imitation procedure was established to examine the development of recall memory in infancy and early childhood. This procedure has been widely used to establish a solid foundation of the nature of recall memory in infancy and early childhood.

The ability to recall the past allows us to report on details of previous experiences, from the everyday to the significant. Because recall memory is ...

Creating Objects and Object Categories for Studying Perception and Perceptual Learning

In order to quantitatively study object perception, be it perception by biological systems or by machines, one needs to create objects and object categories with precisely definable, preferably naturalistic, properties1. Furthermore, for studies on perceptual learning, it is useful to create novel objects and object categories (or object classes) with such properties2.
Many innovative and useful methods currently exist for creating novel objects and object categories3-6 (also see refs. 7,8). However, generally speaking, the existing methods have three broad types of shortcomings.
First, shape variations are generally imposed by the experimenter5,9,10, and may therefore be different from the variability in natural categories, and optimized for a particular recognition algorithm. It would be desirable to have the variations arise independently of the externally imposed constraints.
Second, the existing methods have difficulty capturing the shape complexity of natural objects11-13. If the goal is to study natural object perception, it is desirable for objects and object categories to be naturalistic, so as to avoid possible confounds and special cases.
Third, it is generally hard to quantitatively measure the available information in the stimuli created by conventional methods. It would be desirable to create objects and object categories where the available information can be precisely measured and, where necessary, systematically manipulated (or 'tuned'). This allows one to formulate the underlying object recognition tasks in quantitative terms.
Here we describe a set of algorithms, or methods, that meet all three of the above criteria. Virtual morphogenesis (VM) creates novel, naturalistic virtual 3-D objects called 'digital embryos' by simulating the biological process of embryogenesis14. Virtual phylogenesis (VP) creates novel, naturalistic object categories by simulating the evolutionary process of natural selection9,12,13. Objects and object categories created by these simulations can be further manipulated by various morphing methods to generate systematic variations of shape characteristics15,16. The VP and morphing methods can also be applied, in principle, to novel virtual objects other than digital embryos, or to virtual versions of real-world objects9,13. Virtual objects created in this fashion can be rendered as visual images using a conventional graphical toolkit, with desired manipulations of surface texture, illumination, size, viewpoint and background. The virtual objects can also be 'printed' as haptic objects using a conventional 3-D prototyper.
We also describe some implementations of these computational algorithms to help illustrate the potential utility of the algorithms. It is important to distinguish the algorithms from their implementations. The implementations are demonstrations offered solely as a 'proof of principle' of the underlying algorithms. It is important to note that, in general, an implementation of a computational algorithm often has limitations that the algorithm itself does not have.
Together, these methods represent a set of powerful and flexible tools for studying object recognition and perceptual learning by biological and computational systems alike. With appropriate extensions, these methods may also prove useful in the study of morphogenesis and phylogenesis.

We describe a novel methodology for creating naturalistic 3-D objects and object categories with precisely defined feature variations. We use simulations of the biological processes of morphogenesis and phylogenesis to create novel, naturalistic virtual 3-D objects and object categories that can then be rendered as visual images or haptic objects.

In order to quantitatively study object perception, be it perception by biological systems or by machines, one needs to create objects and object ...

Neuroscience

Defining the Role Of Language in Infants' Object Categorization with Eye-tracking Paradigms

Assessing infant category learning is a challenging but vital aspect of studying infant cognition. By employing a familiarization-test paradigm, we straightforwardly measure infants&#8217; success in learning a novel category while relying only on their looking behavior. Moreover, the paradigm can directly measure the impact of different auditory signals on the infant categorization across a range of ages. For instance, we assessed how 2-year-olds learn categories in a variety of labeling environments: in our task, 2-year-olds successfully learned categories when all exemplars were labeled&#160;or the first two exemplars were labeled, but they failed to categorize when no exemplars were labeled or only the final two exemplars were labeled. To determine infants&#8217; success in such tasks, researchers can examine both the overall preference displayed by infants in each condition and infants&#8217; pattern of looking over the course of the test phase, using an eye-tracker to provide fine-grained time-course data. Thus, we present a powerful paradigm for identifying the role of language, or any auditory signal, in infants&#8217; object category learning.

Here we present a protocol for familiarization-test paradigms which provide a direct test of infant categorization and help to define the role of language in early category learning.

Assessing infant category learning is a challenging but vital aspect of studying infant cognition. By employing a familiarization-test paradigm, we ...

Exploring Infant Sensitivity to Visual Language using Eye Tracking and the Preferential Looking Paradigm

We discuss the use of the preferential looking paradigm in eye tracking studies in order to study how infants develop, understand, and attend to the world around them. Eye tracking is a safe and non-invasive way to collect gaze data from infants, and the preferential looking paradigm is simple to design and only requires the infant to be attending to the screen. By simultaneously showing two visual stimuli that differ in one dimension, we can assess whether infants show different looking behavior for either stimulus, thus demonstrating sensitivity to that difference. The challenges in such experimental approaches are that experiments must be kept brief (no more than 10 min) and be carefully controlled such that the two stimuli differ in only one way. The interpretation of null results must also be carefully considered. In this paper, we illustrate a successful example of an infant eye tracking study with a preferential looking paradigm to discover that 6-month-olds are sensitive to linguistic cues in a signed language despite having no prior exposure to signed language, suggesting that infants possess intrinsic or innate sensitivities to these cues.

Eye tracking studies using a preferential looking paradigm can be used to study infants&#39;&#160;emerging understanding of, and attention to, their external visual world.

We discuss the use of the preferential looking paradigm in eye tracking studies in order to study how infants develop, understand, and attend to the world ...

Habituation: Studying Infants Before They Can Talk

Source: Laboratories of Nicholaus Noles, Judith Danovitch, and Cara Cashon&#8212;University of Louisville
Infants are one of the purest sources of information about human thinking and learning, because they&#8217;ve had very few life experiences. Thus, researchers are interested in gathering data from infants, but as participants in experimental research, they are a challenging group to study. Unlike older children and adults, young infants are unable to reliably speak, understand speech, or even move and control their own bodies. Eating, sleeping, and looking around are the only activities babies can perform reliably. Given these limitations, researchers have developed clever techniques for exploring infants&#8217; thoughts. One of the most popular methods makes use of a characteristic of attention called habituation.
Like adults, infants prefer to pay attention to new and interesting things. If they are left in the same environment, over time they become accustomed to their surroundings and pay less attention to them. This process is called habituation. However, the moment something new happens, infants are waiting and ready to pay attention again. This reengagement of attention following habituation is referred to as dishabituation. Scientists can use these characteristic changes in attention as a tool for studying the thinking and learning of young infants. This method involves initially presenting stimuli to infants until they are habituated, and then presenting them with different kinds of stimuli to see if they dishabituate, i.e., notice a change. By carefully choosing the stimuli shown to the infants, researchers can learn a great deal about how infants think and learn.
This experiment demonstrates how habituation can be used to study infant shape discrimination.

Source: Laboratories of Nicholaus Noles, Judith Danovitch, and Cara Cashon&#8212;University of Louisville
Infants are one of the purest sources of ...

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Psychology

Developmental Psychology

Mutual Exclusivity: How Children Learn the Meanings of Words

Source: Laboratories of Nicholaus Noles and Judith Danovitch&#8212;University of Louisville
Humans are different from other animals in many ways, but perhaps the most important differentiating factor is their ability to use language. Other animals can communicate and even understand and use language in limited ways, but trying to teach human language to a chimp or a dog takes a great deal of time and effort. In contrast, young humans acquire their native language easily, and they learn linguistic rules without explicit instruction, which is an accomplishment that even the smartest animals cannot match.&#160;
One advantage young humans have over animals is that the human brain is especially adapted to learn new words. With only a few exposures, young children can learn new words and remember them. Perhaps more impressively, children can use what they already know to guide their future learning. For example, children treat objects as if they have only one label. So, if a child has learned the word hammer, they won&#8217;t assume an unfamiliar tool has the same name. This is the principle of mutual exclusivity.1-2
This video demonstrates children&#8217;s ability to use mutual exclusivity to match words to objects in their environment.

Source: Laboratories of Nicholaus Noles and Judith Danovitch&#8212;University of Louisville
Humans are different from other animals in many ways, but ...

Categories and Inductive Inferences

Source: Laboratories of Nicholaus Noles and Judith Danovitch&#8212;University of Louisville
It might be possible for the human brain to keep track of each individual person, place, or thing encountered, but that would be a very inefficient use of time and cognitive resources. Instead, humans develop categories. Categories are mental representations of real things that can be used for a variety of purposes. For example, individuals can use the perceptual features of animals to place them into a given category. So, upon seeing a furry, four-legged, tail-wagging, barking animal, a person can determine that it is a dog. This is one of many examples where people use perceptual similarity to fit new experiences into their existing mental representations.
However, category membership is much more than skin deep, especially for representations of animals. Frank Keil demonstrated this by using a simple, yet powerful technique that focused on the differences between natural kinds and artifacts. Natural kinds include animals and other living things, while artifacts consist largely of nonliving things, such as tables or gold bricks. In his study, Keil told children stories about natural kinds and artifacts that underwent transformations causing them to cross categorical boundaries. For example, he described a step-by-step process by which a raccoon was transformed into a creature that resembled a skunk in every way. At the end of the story, the raccoon was black with a white stripe, and it had implanted glands that made it smell like a skunk, too. He asked the children to determine whether the resulting animal was a raccoon or a skunk. He used a similar method to describe the transformation of a tire-an artifact-into a shoe. Children&#39;s responses revealed interesting developmental changes into how people think about artifacts and natural kinds.
This video demonstrates Frank Keil&#39;s transformation study.1

How Children Categorize Objects and Make Inductive Inferences

Source: Laboratories of Nicholaus Noles and Judith Danovitch&#8212;University of Louisville
It might be possible for the human brain to keep track of each ...

Language Development

Children master language quickly and with relative ease, supported by both biological predisposition and reinforcement. B. F. Skinner (1957) proposed that language is learned through reinforcement, while Noam Chomsky (1965) argued that language acquisition mechanisms are biologically determined.
The critical period for language acquisition suggests that the ability to acquire language is at its peak early in life. As people age, this proficiency decreases. Language development begins very early, even before birth. Newborns show a preference for their mother&#39;s voice and can discriminate between their mother&#39;s language and other languages. Babies are attuned to the languages around them and prefer synchronized audio-visual language stimuli.
Initially, babies can differentiate among the sounds of all human languages. However, by around one year old, they can only discriminate among the phonemes used in their environment. After the first few months, babies enter the babbling stage, producing repeated single syllables. This babbling is not necessarily communicative and can occur when babies are alone. Babies exposed to sign language will also babble with their hands.
Children typically utter their first word between 1 year and 18 months, entering the &#34;one-word&#34; stage where single words carry larger meanings. Early vocabulary is often limited to familiar objects or events, primarily nouns. As children&#39;s vocabulary grows, they begin to form simple sentences and rapidly acquire new words. They also demonstrate an understanding of language rules, sometimes making mistakes through overgeneralization, such as saying &#34;gooses&#34; instead of &#34;geese.&#34;
Children&#39;s language development follows a consistent pattern across different cultures and backgrounds, suggesting a biological predisposition for language acquisition. Here&#39;s an overview of the developmental stages:
<ol style="list-style-type: circle;">
	<li>0-3 months: Babies engage in reflexive communication, responding to stimuli without intentionality.</li>
	<li>3-8 months: Reflexive communication continues, with an emerging interest in others and their interactions.</li>
	<li>8-13 months: Intentional communication and sociability develop as babies begin to understand that sounds can have meaning and purpose.</li>
	<li>12-18 months: The first words are typically spoken. These early words are often simple and related to familiar objects or people.</li>
	<li>18-24 months: Children start to form simple sentences of two words, combining basic concepts like &#34;want cookie&#34; or &#34;big truck.&#34;</li>
	<li>2-3 years: Sentences become more complex, consisting of three or more words. Vocabulary rapidly expands during this stage.</li>
	<li>3-5 years: Children are capable of forming complex sentences and engaging in conversations. Their language use becomes more sophisticated, and they have a better grasp of grammar and syntax.</li>
</ol>
This progression from reflexive sounds to complex sentences illustrates the remarkable ability of children to acquire language, guided by both biological predispositions and environmental interactions.

Children master language quickly, aided by biological predisposition and reinforcement.
Skinner proposed language learning through reinforcement, while ...

KEY TERMS AND CONCEPTS

The Nativist Approach

The nativist approach to infant cognitive development proposes that infants are born with inherent knowledge structures that allow them to interpret the world almost immediately. This perspective contrasts with earlier developmental theories, such as those proposed by Jean Piaget, which emphasized a more gradual acquisition of cognitive abilities through interaction with the environment. One key concept in this approach is object permanence &#8212; the understanding that objects continue to exist even when out of view. Nativist research has revealed that infants as young as three to four months demonstrate an expectation that objects are substantial, meaning they resist interference from other objects and persist in time and space. This finding challenges Piaget&#39;s assertion that object permanence emerges only between five to eight months of environmental interaction.
The nativist framework is exemplified by Elizabeth Spelke&#39;s core knowledge theory, which argues that infants possess domain-specific systems of knowledge at birth. Spelke&#39;s research identifies four primary domains: object representation, spatial navigation, numerical sense, and language. Each domain contains specialized, evolutionarily adapted cognitive processes that prepare infants for survival and interaction with their surroundings. For instance, infants demonstrate an intuitive grasp of spatial relationships, an elementary sense of numbers, and sensitivity to the properties of physical objects. According to core knowledge theory, this predisposed knowledge base allows infants to interpret basic environmental cues and lays the groundwork for complex learning and cognitive development.
The core knowledge theory is heavily influenced by evolutionary psychology, suggesting that cognitive structures evolved to equip humans with survival-relevant skills from an early age. The prewiring of knowledge domains like object permanence and spatial awareness serves to optimize infants&#39; ability to navigate their environment, interact with others, and process information relevant to survival.
However, the nativist approach has received criticism for potentially overlooking the role of social and environmental influences in cognitive development. Critics argue that while innate structures may guide infants&#39; interactions with their surroundings, external factors &#8212; particularly social interactions &#8212; play a significant role in shaping and enhancing early cognition.

The Nativist approach to infant cognitive development suggests that infants are born with significant knowledge and understanding of the world.
For ...

Experience is Instrumental in Tuning a Link Between Language and Cognition: Evidence from 6- to 7- Month-Old Infants' Object Categorization

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