This work was supported by NIH R01 EY028915 (TI) and RPB grants.

All experiments and animal care were conducted in accordance with protocol approved by the Institutional Animal Care and Use Committees at Wayne State University (protocol no. 17-11-0399).
1. Preparation for the experiment
<ol>
	<li>Build a rectangular open-lid enclosure to house the mouse during looming visual stimuli presentation. We constructed a 40 cm x 50 cm x 33 cm enclosure using aluminum framing and PVC panels (Figure 1A,B). Lay a sheet of paper to cover the entire floor of the enclosure to ensure easy cleanup between trials. Add an opaque shelter in a corner of the enclosure with an entrance facing the center of the arena for easy entrance and exit.</li>
	<li>Set up a camera with a wide-angle lens for capturing the mouse&#8217;s behavior. Secure the camera to a table-mounted stand adjacent to the enclosure. For best quality video capturing, use a camera frame rate of 60 FPS or higher.</li>
	<li>Set up a computer monitor on top of the enclosure. Because the monitor could not be seen from the outside, a second monitor was prepared, which duplicated the images shown on the primary monitor.</li>
	<li>Prepare a looming pattern for projection. One way to do this is to use the PsychToolbox3 within MatLab software to code for an expanding black circle (Figure 1C). Set the stimulus to begin at a visual angle of 2&#176; and expand to 50&#176; over 250 ms; these parameters determine stimulus speed (see Figure 1D for visual angle calculation). Set the code to repeat the stimulus 10 times with an interval of 1 s. 
	NOTE: The stimulus began each repetition immediately upon termination of the previous presentation. For further information on stimulus presentation, please refer to section 3.</li>
	<li>Select mice of interest for the looming stimuli. Here, use 32 healthy-eyed mice of a C57 background, male and female, 4 to 14 weeks old. Also, use 3 blind mice (severe cataracts in both eyes) to assess whether the response to looming stimulus was truly a visually guided behavior. These blind mice had no pupillary light reflex and no optomotor response.</li>
</ol>
2. Mouse acclimation
<ol>
	<li>Place a mouse in the enclosure and let it freely explore its surroundings. If possible, try to minimize stress during animal transfer by using the back of your free hand as a resting place for the mouse instead of letting it hang without support. The mouse should find the entire enclosure to be safe and should discover the hiding place. Drop a few food pellets in the corner opposite the refuge to encourage the mouse to remain outside the refuge.</li>
	<li>Allow the mouse to acclimate anywhere from 7 to 15 min29,39. We allowed 10 min of acclimation prior to stimulus onset. Furthermore, 10 min acclimation one day prior to the experiment may ease the mice.</li>
</ol>
3. Looming visual stimuli projection
<ol>
	<li>Prior to inserting the mouse into the arena, make sure the stimulus code is ready to run to facilitate as few lighting changes as possible while the mouse is in the enclosure. Once the software is ready to run, gently place the mouse in the enclosure.</li>
	<li>10 seconds prior to the stimulation, start the video capturing.</li>
	<li>Start the looming visual stimuli when the mouse is away from the shelter and moving freely in the open arena. Wait 10 seconds after the last stimulus presentation to terminate the recording.
	<ol>
		<li>Begin the stimulus presentation when the mouse is in the corner farthest from the refuge. However, when mice seem unwilling to explore the far corner, present the stimulus when the mouse is in a different corner of the arena. This does not appear to make a difference in animal behavioral response.</li>
	</ol>
	</li>
	<li>Transfer the mouse back to its original cage. Clean the enclosure for the next mouse by spraying the walls and refuge with 70% ethanol and wiping it down. Replace the paper floor liner if soiled and reposition the refuge to the same initial location if moved during animal transfer and enclosure cleaning.</li>
</ol>
4. Video analysis
<ol>
	<li>Save the video clip for each mouse in .avi format without file compression in order to ensure no data loss during transfer to the analysis software. 
	NOTE: Lack of compression will lead to larger file size; therefore, use external hard drive for storage.</li>
	<li>Use analysis software to track the animal&#8217;s motion around the arena prior to, during, and after stimulus presentation. Use commercially available software (see Table of Materials) with a manual tracking ability to track the position of the mouse head in every video frame, which generated X and Y coordination every 1/60 ms. Other motion-tracking software includes FIJI (NIH)40 and EthoVision (Noldus).</li>
	<li>Calculate the velocity and the distance of the mouse from the refuge. If the image of the arena is distorted due to the video angle, correct the X and Y coordination prior to the calculation (Figure 2).</li>
	<li>Compare the parameters before and after looming stimulus onset to determine how the mouse responded to the stimuli, whether by freezing, fleeing, or demonstrating no change in behavior29. Define freezing as episodes where speed was less than 20 mm/s for 0.5 s or longer. Define flight as episodes where speed increased to 400 mm/s or greater and ended with the mouse in the refuge. Definitions for freezing and flight were based on those set by Franceschi et al.29</li>
</ol>

<ol>
	<li>Enroth-Cugell, C., Robson, J. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+contrast+sensitivity+of+retinal+ganglion+cells+of+the+cat.">The contrast sensitivity of retinal ganglion cells of the cat.</a> The Journal of Physiology. 187 (3), 517-552 (1966).</li><li>Boycott, B. B., W&#228;ssle, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+morphological+types+of+ganglion+cells+of+the+domestic+cat's+retina.">The morphological types of ganglion cells of the domestic cat's retina.</a> The Journal of Physiology. 240 (2), 397-419 (1974).</li><li>Livingstone, M. S., Hubel, D. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Segregation+of+form,+color,+movement,+and+depth:+anatomy,+physiology,+and+perception.">Segregation of form, color, movement, and depth: anatomy, physiology, and perception.</a> Science. 240 (4853), 740-749 (1988).</li><li>Livingstone, M. S., Hubel, D. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Psychophysical+evidence+for+separate+channels+for+the+perception+of+form,+color,+movement,+and+depth.">Psychophysical evidence for separate channels for the perception of form, color, movement, and depth.</a> The Journal of Neuroscience. 7 (11), 3416-3468 (1987).</li><li>W&#228;ssle, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Parallel+processing+in+the+mammalian+retina.">Parallel processing in the mammalian retina.</a> Nature Reviews Neuroscience. 5 (10), 747-757 (2004).</li><li>Awatramani, G. B., Slaughter, M. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Origin+of+transient+and+sustained+responses+in+ganglion+cells+of+the+retina.">Origin of transient and sustained responses in ganglion cells of the retina.</a> The Journal of Neuroscience. 20 (18), 7087-7095 (2000).</li><li>Ghosh, K. K., Bujan, S., Haverkamp, S., Feigenspan, A., W&#228;ssle, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Types+of+bipolar+cells+in+the+mouse+retina.">Types of bipolar cells in the mouse retina.</a> The Journal of Comparative Neuroscience. 469 (1), 70-82 (2004).</li><li>W&#228;ssle, H., Puller, C., Muller, F., Haverkamp, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cone+contacts,+mosaics,+and+territories+of+bipolar+cells+in+the+mouse+retina.">Cone contacts, mosaics, and territories of bipolar cells in the mouse retina.</a> The Journal of Neuroscience. 29 (1), 106-117 (2009).</li><li>Helmstaedter, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Connectomic+reconstruction+of+the+inner+plexiform+layer+in+the+mouse+retina.">Connectomic reconstruction of the inner plexiform layer in the mouse retina.</a> Nature. 500 (7461), 168-174 (2013).</li><li>Shekhar, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comprehensive+Classification+of+Retinal+Bipolar+Neurons+by+Single-Cell+Transcriptomics.">Comprehensive Classification of Retinal Bipolar Neurons by Single-Cell Transcriptomics.</a> Cell. 166 (5), 1308-1323 (2016).</li><li>Wu, S. M., Gao, F., Maple, B. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+architecture+of+synapses+in+the+inner+retina:+segregation+of+visual+signals+by+stratification+of+bipolar+cell+axon+terminals.">Functional architecture of synapses in the inner retina: segregation of visual signals by stratification of bipolar cell axon terminals.</a> The Journal of Neuroscience. 20 (12), 4462-4470 (2000).</li><li>Sun, W., Li, N., He, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Large-scale+morphological+survey+of+mouse+retinal+ganglion+cells.">Large-scale morphological survey of mouse retinal ganglion cells.</a> The Journal of Comparative Neuroscience. 451 (2), 115-126 (2002).</li><li>Volgyi, B., Chheda, S., Bloomfield, S. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tracer+coupling+patterns+of+the+ganglion+cell+subtypes+in+the+mouse+retina.">Tracer coupling patterns of the ganglion cell subtypes in the mouse retina.</a> The Journal of Comparative Neuroscience. 512 (5), 664-687 (2009).</li><li>Kong, J. H., Fish, D. R., Rockhill, R. L., Masland, R. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diversity+of+ganglion+cells+in+the+mouse+retina:+Unsupervised+morphological+classification+and+its+limits.">Diversity of ganglion cells in the mouse retina: Unsupervised morphological classification and its limits.</a> The Journal of Comparative Neuroscience. 489 (3), 293-310 (2005).</li><li>Sumbul, U., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+genetic+and+computational+approach+to+structurally+classify+neuronal+types.">A genetic and computational approach to structurally classify neuronal types.</a> Nature Communications. 5, 3512 (2014).</li><li>Baden, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+functional+diversity+of+retinal+ganglion+cells+in+the+mouse.">The functional diversity of retinal ganglion cells in the mouse.</a> Nature. 529 (7586), 345-350 (2016).</li><li>Lindstrom, S. H., Ryan, D. G., Shi, J., DeVries, S. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kainate+receptor+subunit+diversity+underlying+response+diversity+in+retinal+Off+bipolar+cells.">Kainate receptor subunit diversity underlying response diversity in retinal Off bipolar cells.</a> The Journal of Physiology. 592, 1457-1477 (2014).</li><li>Euler, T., Haverkamp, S., Schubert, T., Baden, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Retinal+bipolar+cells:+elementary+building+blocks+of+vision.">Retinal bipolar cells: elementary building blocks of vision.</a> Nature Reviews Neuroscience. 15 (8), 507-519 (2014).</li><li>Yoshida, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+key+role+of+starburst+amacrine+cells+in+originating+retinal+directional+selectivity+and+optokinetic+eye+movement.">A key role of starburst amacrine cells in originating retinal directional selectivity and optokinetic eye movement.</a> Neuron. 30 (3), 771-780 (2001).</li><li>Pearson, R. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Restoration+of+vision+after+transplantation+of+photoreceptors.">Restoration of vision after transplantation of photoreceptors.</a> Nature. 485 (7396), 99-103 (2012).</li><li>Saszik, S. M., Robson, J. G., Frishman, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+scotopic+threshold+response+of+the+dark-adapted+electroretinogram+of+the+mouse.">The scotopic threshold response of the dark-adapted electroretinogram of the mouse.</a> The Journal of Physiology. 543, 899-916 (2002).</li><li>Reuter, J. H., Sanyal, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+and+degeneration+of+retina+in+rds+mutant+mice:+the+electroretinogram.">Development and degeneration of retina in rds mutant mice: the electroretinogram.</a> Neuroscience Letters. 48 (2), 231-237 (1984).</li><li>Woodward, W. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isoflurane+is+an+effective+alternative+to+ketamine/xylazine/acepromazine+as+an+anesthetic+agent+for+the+mouse+electroretinogram.">Isoflurane is an effective alternative to ketamine/xylazine/acepromazine as an anesthetic agent for the mouse electroretinogram.</a> Documenta Ophthalmologica. 115 (3), 187-201 (2007).</li><li>Cahill, H., Nathans, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+optokinetic+reflex+as+a+tool+for+quantitative+analyses+of+nervous+system+function+in+mice:+application+to+genetic+and+drug-induced+variation.">The optokinetic reflex as a tool for quantitative analyses of nervous system function in mice: application to genetic and drug-induced variation.</a> PLoS One. 3 (4), 2055 (2008).</li><li>Prusky, G. T., Alam, N. M., Beekman, S., Douglas, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+quantification+of+adult+and+developing+mouse+spatial+vision+using+a+virtual+optomotor+system.">Rapid quantification of adult and developing mouse spatial vision using a virtual optomotor system.</a> Investigative Ophthalmology &amp; Visual Science. 45 (12), 4611-4616 (2004).</li><li>Lu, Q., Ganjawala, T. H., Hattar, S., Abrams, G. W., Pan, Z. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Robust+Optomotor+Assay+for+Assessing+the+Efficacy+of+Optogenetic+Tools+for+Vision+Restoration.">A Robust Optomotor Assay for Assessing the Efficacy of Optogenetic Tools for Vision Restoration.</a> Investigative Ophthalmology &amp; Visual Science. 59 (3), 1288-1294 (2018).</li><li>Xue, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Melanopsin+signalling+in+mammalian+iris+and+retina.">Melanopsin signalling in mammalian iris and retina.</a> Nature. 479 (7371), 67-73 (2011).</li><li>Yilmaz, M., Meister, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+innate+defensive+responses+of+mice+to+looming+visual+stimuli.">Rapid innate defensive responses of mice to looming visual stimuli.</a> Current Biology. 23 (20), 2011-2015 (2013).</li><li>De Franceschi, G., Vivattanasarn, T., Saleem, A. B., Solomon, S. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vision+Guides+Selection+of+Freeze+or+Flight+Defense+Strategies+in+Mice.">Vision Guides Selection of Freeze or Flight Defense Strategies in Mice.</a> Current Biology. 26 (16), 2150-2154 (2016).</li><li>Temizer, I., Donovan, J. C., Baier, H., Semmelhack, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Visual+Pathway+for+Looming-Evoked+Escape+in+Larval+Zebrafish.">A Visual Pathway for Looming-Evoked Escape in Larval Zebrafish.</a> Current Biology. 25 (14), 1823-1834 (2015).</li><li>Guest, B. B., Gray, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Responses+of+a+looming-sensitive+neuron+to+compound+and+paired+object+approaches.">Responses of a looming-sensitive neuron to compound and paired object approaches.</a> Journal of Neurophysiology. 95 (3), 1428-1441 (2006).</li><li>McMillan, G. A., Gray, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+looming-sensitive+pathway+responds+to+changes+in+the+trajectory+of+object+motion.">A looming-sensitive pathway responds to changes in the trajectory of object motion.</a> Journal of Neurophysiology. 108 (4), 1052-1068 (2012).</li><li>Vagnoni, E., Lourenco, S. F., Longo, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Threat+modulates+neural+responses+to+looming+visual+stimuli.">Threat modulates neural responses to looming visual stimuli.</a> Eur The Journal of Neuroscience. 42 (5), 2190-2202 (2015).</li><li>Coker-Appiah, D. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Looming+animate+and+inanimate+threats:+the+response+of+the+amygdala+and+periaqueductal+gray.">Looming animate and inanimate threats: the response of the amygdala and periaqueductal gray.</a> Social Neuroscience. 8 (6), 621-630 (2013).</li><li>Tyll, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neural+basis+of+multisensory+looming+signals.">Neural basis of multisensory looming signals.</a> Neuroimage. 65, 13-22 (2013).</li><li>Wei, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Processing+of+visually+evoked+innate+fear+by+a+non-canonical+thalamic+pathway.">Processing of visually evoked innate fear by a non-canonical thalamic pathway.</a> Nature Communications. 6, 6756 (2015).</li><li>Shang, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Divergent+midbrain+circuits+orchestrate+escape+and+freezing+responses+to+looming+stimuli+in+mice.">Divergent midbrain circuits orchestrate escape and freezing responses to looming stimuli in mice.</a> Nature Communications. 9 (1), 1232 (2018).</li><li>Salay, L. D., Ishiko, N., Huberman, A. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+midline+thalamic+circuit+determines+reactions+to+visual+threat.">A midline thalamic circuit determines reactions to visual threat.</a> Nature. 557 (7704), 183-189 (2018).</li><li>Vale, R., Evans, D., Branco, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Behavioral+Assay+for+Investigating+the+Role+of+Spatial+Memory+During+Instinctive+Defense+in+Mice.">A Behavioral Assay for Investigating the Role of Spatial Memory During Instinctive Defense in Mice.</a> Journal of Visualized Experiments. (137), 56988 (2018).</li><li>Tungtur, S. K., Nishimune, N., Radel, J., Nishimune, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mouse+Behavior+Tracker:+An+economical+method+for+tracking+behavior+in+home+cages.">Mouse Behavior Tracker: An economical method for tracking behavior in home cages.</a> Biotechniques. 63 (5), 215-220 (2017).</li></ol>

The authors have nothing to disclose.

With the looming visual stimuli system, a majority (97%) of healthy eye-mice showed flight response. One of 29 mice did not show an obvious flight response. However, the mouse walked toward the dome and remained near it until looming disappeared, indicating that the mouse was at least cautious when the looming stimuli occurred. Therefore, the looming stimuli consistently elicited innate fear responses in healthy-eyed mice. On the other hand, three blind mice did not show any responses to the looming (preliminary results)...

The visual system starts at the retina, where visual signals are captured by photoreceptors, channeled to bipolar cells (2nd-order neurons), and finally passed to ganglion cells (3rd-order neurons). Retinal 2nd- and 3rd-order neurons are thought to form multiple neural pathways that convey particular aspects of visual signaling such as color, motion, or shape. These diverse visual features are relayed to the lateral geniculate nucleus and the visual cortex. In contrast, visual signals leading to eye movement are sent to the superior colliculus. Classically, two retino-cortical pathways have been identified: the magnocellular and the parvocellular pathways. These pathways encode moving and stationary objects, respectively, and their existence embodies the basic concept of parallel processing1,2,3,4,5,6. Recently, more than 15 types of bipolar cells7,8,9,10,11 and ganglion cells12,13,14,15,16 have been reported in the retina of many species, including the primate retina. These cells are distinguished not only by morphological aspects, but also by the expression of distinct markers and genes8,10,17,18, suggesting that various features of visual signals are processed in parallel, which is more complicated than originally anticipated.
Cellular and molecular technologies have contributed to our understanding of visual processing and potential disease mechanisms that may arise from aberrant visual processing. Such an understanding may contribute to the development of artificial eyes. Although cellular examinations and analysis offer in-depth knowledge at a cellular level, a combination of behavioral experiments and cellular experiments would significantly augment our current understanding of minute visual processes. For example, Yoshida et al.19 found that starburst amacrine cells are the key neurons for motion detection in the mouse retina. Following cellular experiments, they performed the optokinetic nystagmus (OKN) behavioral experiment to show that mutant mice in which starburst amacrine cells were dysfunctional did not respond to moving objects, thereby confirming their cellular investigations. In addition, Pearson et al.20 conducted photoreceptor transplantation in the mouse retina to restore vision in diseased mice. They conducted not only cellular experiments, but also measured mouse behavior through the use of optomotor response recordings and water-maze tasks thus allowing Pearson et al. to verify that transplanted photoreceptors restored vision in the formerly blind mice. Taken together, behavioral experiments are strong tools to assess mouse vision.
Multiple methods are available for measuring mouse vision. These methods have advantages and limitations. In vivo ERG provides information on whether the mouse retina, particularly photoreceptors and ON bipolar cells, appropriately responds to light stimuli. ERG can be tested either under scotopic or photopic conditions21,22. However, ERG requires anesthesia, which might affect the output measurement23. The optokinetic reflex (OKR) or optomotor response (OMR) is a robust method to assess contrast sensitivity and spatial resolution, both functional components of mouse vision. However, OKR requires surgery to attach a fixation device to the mouse skull24. OMR requires neither surgery nor mouse training; however, it requires training to allow an experimenter to subjectively detect subtle mouse head movements in response to a moving grating in an optic drum 25,26. Pupil light reflex measures pupil constriction in response to light stimuli, which does not require anesthesia and exhibits objective and robust responses 19. Although the pupil reflex simulates retinal light response in vivo, the reflex is mediated mainly by the intrinsically photosensitive retinal ganglion cells (ipRGCs) 27. Because ipRGCs represent a small minority of RGCs and do not serve as conventional image-forming ganglion cells, this measurement does not provide information pertaining to the majority of ganglion cells.
The looming light experiment has not previously been considered a major test for measuring mouse vision. However, it is also a robust and reliable vision test across various species, such as mouse28,29, zebrafish30, locust31,32, and human33,34,35. Importantly, the looming experiment is one of only a few methods to test the image-forming pathway - it is not a reflex pathway - given the visual and the limbic systems in the central nervous system are involved in this circuit36,37,38. We have established a looming visual stimulus system and have demonstrated its ability to elicit motion detection in the mouse, which we use as a proxy to assess the intactness of the mouse visual system.

<table border="0" cellpadding="0" cellspacing="0" style="width:1349px;" width="1350">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:299px;">10.1&#34; monitor (2&#176; display)</td>
			<td style="width:148px;">Elecrow</td>
			<td style="width:903px;">Elecrow 10.1 Inch Raspberry Pi 1920x1080p Resolution Display</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">14&#34; Business Class Laptop 5490</td>
			<td>Dell</td>
			<td>84 / rcrc961481-4860836</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">20&#34; x 50&#34; Absorbant Liners</td>
			<td>Fisher Scientific</td>
			<td>AL2050</td>
			<td>works well to protect floor of arena, could use any type of liner</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">21.5&#34; monitor (1&#176; display)</td>
			<td>Acer</td>
			<td>Acer R221Q bid 21.5-inch IPS Full HD Display</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">CCD Camera</td>
			<td>Lumenera Corporation</td>
			<td>Infiniyy3S-1UR</td>
			<td>excellent for behavioral studies due to high fps rate (60 fps)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Enclosure (alminum frames and PVC panels)</td>
			<td>80/20 Inc.</td>
			<td>4x cat.#9010, 4x cat.#9005, 1x cat.#9000, 5x cat.#65-2616</td>
			<td>excellent, used quick build tab to find PVC, joints, and frame</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ethanol</td>
			<td>Fisher Scientific</td>
			<td>22-032-601</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Excel Spreadsheet Software</td>
			<td>Microsoft Office</td>
			<td></td>
			<td>user friendly and widespread knowledge of Microsoft Office software</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Freearm</td>
			<td>Amazon</td>
			<td></td>
			<td>used to mount camera to the table, could use any mountable extendable arm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">ImagePro Premiere 3D</td>
			<td>Media Cybernetics</td>
			<td>version 9.3</td>
			<td>good program, could use some updating with the automated tracking feature</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Matlab software (Psychotoolbox 3)</td>
			<td>MathWorks</td>
			<td>Matlab R2018b 64-bit (9.5.0.944444)</td>
			<td>excellent software to generate pattern stimuli of any conditions</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">SteamPix sorftware</td>
			<td>Norpix</td>
			<td>StreamPix 7 64-bit Single Camera</td>
			<td>works well, a few problems with frame dropping but good customer service</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">WD My Book External Hard Drive</td>
			<td>Western Digital</td>
			<td>WDBBGB0080HBK hard drive 8 TB USB 3.0</td>
			<td>necessary if using .avi files with no compression codec due to large size of files</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Wide angle lens</td>
			<td>Navitar</td>
			<td>NMV-5M23</td>
			<td>excellent and necessary to capture entire arena</td>
		</tr>
	</tbody>
</table>

using looming visual stimuli to evaluate mouse vision

The visual system in the central nervous system processes diverse visual signals. Although the overall structure has been characterized from the retina through the lateral geniculate nucleus to the visual cortex, the system is complex. Cellular and molecular studies have been conducted to elucidate the mechanisms underpinning visual processing and, by extension, disease mechanisms. These studies may contribute to the development of artificial visual systems. To validate the results of these studies, behavioral vision testing is necessary. Here, we show that the looming stimulation experiment is a reliable mouse vision test that requires a relatively simple setup. The looming experiment was conducted in a large enclosure with a shelter in one corner and a computer monitor located on the ceiling. A CCD camera positioned next to the computer monitor served to observe mouse behavior. A mouse was placed in the enclosure for 10 minutes and allowed to acclimate to and explore the surroundings. Then, the monitor projected a program-derived looming stimulus 10 times. The mouse responded to the stimuli either by freezing or by fleeing to the hiding place. The mouse&#39;s behavior before and after the looming stimuli was recorded, and the video was analyzed using motion tracking software. The velocity of the mouse movement significantly changed after the looming stimuli. In contrast, no reaction was observed in blind mice. Our results demonstrate that the simple looming experiment is a reliable test of mouse vision.

A mouse with healthy eyes was placed in the enclosure and allowed to acclimate for 10 min. The arena with the monitor on the ceiling was kept under mesopic light conditions (7 x 105 photons/&#956;m2/s). During the acclimation period, the mouse explored the space and found the opaque dome as a refuge. When the mouse moved away from the refuge, video capturing started, followed by initiation of the visual stimulus. In response to the looming stimulus, most mice ran into the dome (flight response), whi...

Watch this Scientific Journal Video about Using Looming Visual Stimuli to Evaluate Mouse Vision at JoVE.com

Using Looming Visual Stimuli to Evaluate Mouse Vision

To examine mouse vision, we conducted a looming test. Mice were placed in a large square arena with a monitor on its ceiling. The looming visual stimulus consistently evoked freezing or flight reactions in the mice.

The visual system in the central nervous system processes diverse visual signals. Although the overall structure has been characterized from the retina ...

using-looming-visual-stimuli-to-evaluate-mouse-vision

Research

JoVE Journal

Behavior

11.0K Views.  Wayne State University School of Medicine. To examine mouse vision, we conducted a looming test. Mice were placed in a large square arena with a monitor on its ceiling. The looming visual stimulus consistently evoked freezing or flight reactions in the mice.

Video: Using Looming Visual Stimuli to Evaluate Mouse Vision

Using Eye Movements to Evaluate the Cognitive Processes Involved in Text Comprehension

The present article describes how to use eye tracking methodologies to study the cognitive processes involved in text comprehension. Measuring eye movements during reading is one of the most precise methods for measuring moment-by-moment (online) processing demands during text comprehension. Cognitive processing demands are reflected by several aspects of eye movement behavior, such as fixation duration, number of fixations, and number of regressions (returning to prior parts of a text). Important properties of eye tracking equipment that researchers need to consider are described, including how frequently the eye position is measured (sampling rate), accuracy of determining eye position, how much head movement is allowed, and ease of use. Also described are properties of stimuli that influence eye movements that need to be controlled in studies of text comprehension, such as the position, frequency, and length of target words. Procedural recommendations related to preparing the participant, setting up and calibrating the equipment, and running a study are given. Representative results are presented to illustrate how data can be evaluated. Although the methodology is described in terms of reading comprehension, much of the information presented can be applied to any study in which participants read verbal stimuli.

The present article describes how to use eye tracking methodologies to study the cognitive processes involved in text comprehension. Descriptions of eye tracking equipment, how to develop experimental stimuli, and procedural recommendations are included. The information presented can be applied to most any study using verbal stimuli.

The present article describes how to use eye  tracking methodologies to study the cognitive processes involved in text  comprehension. Measuring eye ...

Irrelevant Stimuli and Action Control: Analyzing the Influence of Ignored Stimuli via the Distractor-Response Binding Paradigm

Selection tasks in which simple stimuli (e.g. letters) are presented and a target stimulus has to be selected against one or more distractor stimuli are frequently used in the research on human action control. One important question in these settings is how distractor stimuli, competing with the target stimulus for a response, influence actions. The distractor-response binding paradigm can be used to investigate this influence. It is particular useful to separately analyze response retrieval and distractor inhibition effects. Computer-based experiments are used to collect the data (reaction times and error rates). In a number of sequentially presented pairs of stimulus arrays (prime-probe design), participants respond to targets while ignoring distractor stimuli. Importantly, the factors response relation in the arrays of each pair (repetition vs. change) and distractor relation (repetition vs. change) are varied orthogonally. The repetition of the same distractor then has a different effect depending on response relation (repetition vs. change) between arrays. This result pattern can be explained by response retrieval due to distractor repetition. In addition, distractor inhibition effects are indicated by a general advantage due to distractor repetition. The described paradigm has proven useful to determine relevant parameters for response retrieval effects on human action.

The distractor-response binding paradigm is described. It can be used to shed light on the influence irrelevant stimuli, competing with targets for a response, can have on human action. Both response retrieval effects and distractor inhibition effects can be analyzed within the paradigm.

Selection tasks in which simple stimuli (e.g. letters) are presented and a target stimulus has to be selected against one or more distractor stimuli are ...

Methods to Test Visual Attention Online

Online data collection methods have particular appeal to behavioral scientists because they offer the promise of much larger and much more representative data samples than can typically be collected on college campuses. However, before such methods can be widely adopted, a number of technological challenges must be overcome &#8211; in particular in experiments where tight control over stimulus properties is necessary. Here we present methods for collecting performance data on two tests of visual attention. Both tests require control over the visual angle of the stimuli (which in turn requires knowledge of the viewing distance, monitor size, screen resolution, etc.) and the timing of the stimuli (as the tests involve either briefly flashed stimuli or stimuli that move at specific rates). Data collected on these tests from over 1,700 online participants were consistent with data collected in laboratory-based versions of the exact same tests. These results suggest that with proper care, timing/stimulus size dependent tasks can be deployed in web-based settings.

To replicate laboratory settings, online data collection methods for visual tasks require tight control over stimulus presentation. We outline methods for the use of a web application to collect performance data on two tests of visual attention.

Online data collection methods have particular appeal to behavioral scientists because they offer the promise of much larger and much more representative ...

Recording Mouse Ultrasonic Vocalizations to Evaluate Social Communication

Mice emit ultrasonic vocalizations in different contexts throughout development and in adulthood. These vocal signals are now currently used as proxies for modeling the genetic bases of vocal communication deficits. Characterizing the vocal behavior of mouse models carrying mutations in genes associated with neuropsychiatric disorders such as autism spectrum disorders will help to understand the mechanisms leading to social communication deficits. We provide here protocols to reliably elicit ultrasonic vocalizations in pups and in adult mice. This standardization will help reduce inter-study variability due to the experimental settings. Pup isolation calls are recorded throughout development from individual pups isolated from dam and littermates. In adulthood, vocalizations are recorded during same-sex interactions (without a sexual component) by exposing socially motivated males or females to an unknown same-sex conspecific. We also provide a protocol to record vocalizations from adult males exposed to an estrus female. In this context, there is a sexual component in the interaction. These protocols are established to elicit a large amount of ultrasonic vocalizations in laboratory mice. However, we point out the important inter-individual variability in the vocal behavior of mice, which should be taken into account by recording a minimal number of individuals (at least 12 in each condition). These recordings of ultrasonic vocalizations are used to evaluate the call rate, the vocal repertoire and the acoustic structure of the calls. Data are combined with the analysis of synchronous video recordings to provide a more complete view on social communication in mice. These protocols are used to characterize the vocal communication deficits in mice lacking ProSAP1/Shank2, a gene associated with autism spectrum disorders. More ultrasonic vocalizations recordings can also be found on the mouseTube database, developed to favor the exchange of such data.

Mouse ultrasonic vocalizations are used as proxies to model the genetic bases of vocal communication deficits in mouse models for neuropsychiatric disorders. The present protocol describes three experimental contexts that reliably elicit ultrasonic vocalizations from pups (throughout development) and adult mice (same-sex interactions, male-estrus female interactions).

Mice emit ultrasonic vocalizations in different contexts throughout development and in adulthood. These vocal signals are now currently used as proxies ...

A Method to Quantify Visual Information Processing in Children Using Eye Tracking

Visual problems that occur early in life can have major impact on a child's development. Without verbal communication and only based on observational methods, it is difficult to make a quantitative assessment of a child's visual problems. This limits accurate diagnostics in children under the age of 4 years and in children with intellectual disabilities. Here we describe a quantitative method that overcomes these problems. The method uses a remote eye tracker and a four choice preferential looking paradigm to measure eye movement responses to different visual stimuli. The child sits without head support in front of a monitor with integrated infrared cameras. In one of four monitor quadrants a visual stimulus is presented. Each stimulus has a specific visual modality with respect to the background, e.g., form, motion, contrast or color. From the reflexive eye movement responses to these specific visual modalities, output parameters such as reaction times, fixation accuracy and fixation duration are calculated to quantify a child's viewing behavior. With this approach, the quality of visual information processing can be assessed without the use of communication. By comparing results with reference values obtained in typically developing children from 0-12 years, the method provides a characterization of visual information processing in visually impaired children. The quantitative information provided by this method can be advantageous for the field of clinical visual assessment and rehabilitation in multiple ways. The parameter values provide a good basis to: (i) characterize early visual capacities and consequently to enable early interventions; (ii) compare risk groups and follow visual development over time; and (iii), construct an individual visual profile for each child.

A method is described to quantify the quality of visual information processing based on reflexive eye movements in response to specific visual modalities. Reaction times and fixation output parameters are used to characterize visual performance in children with and without visual impairments from 6 months of age.

Visual problems that occur early in life can have major impact on a child's development. Without verbal communication and only based on observational ...

Implantation and Recording of Wireless Electroretinogram and Visual Evoked Potential in Conscious Rats

The full-field electroretinogram (ERG) and visual evoked potential (VEP) are useful tools to assess retinal and visual pathway integrity in both laboratory and clinical settings. Currently, preclinical ERG and VEP measurements are performed with anesthesia to ensure stable electrode placements. However, the very presence of anesthesia has been shown to contaminate normal physiological responses. To overcome these anesthesia confounds, we develop a novel platform to assay ERG and VEP in conscious rats. Electrodes are surgically implanted sub-conjunctivally on the eye to assay the ERG and epidurally over the visual cortex to measure the VEP. A range of amplitude and sensitivity/timing parameters are assayed for both the ERG and VEP at increasing luminous energies. The ERG and VEP signals are shown to be stable and repeatable for at least 4 weeks post surgical implantation. This ability to record ERG and VEP signals without anesthesia confounds in the preclinical setting should provide superior translation to clinical data.

We show surgical implantation and Recording procedures to measure visual electrophysiological signals from the eye (electroretinogram) and brain (visual evoked potential) in conscious rats, which is more analogous to the human condition where recordings are conducted without anesthesia confounds.

The full-field electroretinogram (ERG) and visual evoked potential (VEP) are useful tools to assess retinal and visual pathway integrity in both ...

Using a Split-belt Treadmill to Evaluate Generalization of Human Locomotor Adaptation

Understanding the mechanisms underlying locomotor learning helps researchers and clinicians optimize gait retraining as part of motor rehabilitation. However, studying human locomotor learning can be challenging. During infancy and childhood, the neuromuscular system is quite immature, and it is unlikely that locomotor learning during early stages of development is governed by the same mechanisms as in adulthood. By the time humans reach maturity, they are so proficient at walking that it is difficult to come up with a sufficiently novel task to study de novo locomotor learning. The split-belt treadmill, which has two belts that can drive each leg at a different speed, enables the study of both short- (i.e., immediate) and long-term (i.e., over minutes-days; a form of motor learning) gait modifications in response to a novel change in the walking environment. Individuals can easily be screened for previous exposure to the split-belt treadmill, thus ensuring that all experimental participants have no (or equivalent) prior experience. This paper describes a typical split-belt treadmill adaptation protocol that incorporates testing methods to quantify locomotor learning and generalization of this learning to other walking contexts. A discussion of important considerations for designing split-belt treadmill experiments follows, including factors like treadmill belt speeds, rest breaks, and distractors. Additionally, potential but understudied confounding variables (e.g., arm movements, prior experience) are considered in the discussion.

We describe a protocol for investigating human locomotor adaptation using the split-belt treadmill, which has two belts that can drive each leg at a different speed. We specifically focus on a paradigm designed to test the generalization of adapted locomotor patterns to different walking contexts (e.g., gait speeds, walking environments).

Understanding the mechanisms underlying locomotor learning helps researchers and clinicians optimize gait retraining as part of motor rehabilitation. ...

Using Rapid Serial Visual Presentation to Measure Set-Specific Capture, a Consequence of Distraction While Multitasking

This method uses a rapid serial visual presentation (RSVP) paradigm to measure the cost of distraction when participants maintain multiple search goals. The protocol identifies two types of distraction within a single task - contingent attentional capture and set-specific capture - that represent different types of limitations of cognitive processing. Participants search for letters in two or more &#34;target&#34; ink colors (e.g., green and orange) within a continuous RSVP stream of heterogeneously colored letters, while ignoring two peripheral RSVPs of letters. Upon detecting a target, participants are to identify the letter. On some trials, target-colored distractors appear in the periphery just prior to the presentation of a target, causing a drop in target identification performance. Contingent attentional capture is observed by examining performance on trials in which the peripheral distractor is the same color as the target on that trial (e.g., both orange). Set-specific capture is represented by performance on trials in which the peripheral distractor is target-colored (e.g., orange), but not the same color as the target on that trial (e.g., green.) By varying the amount of time (i.e., the number of stimuli appearing) between the presentation of the distractor and the target, researchers can observe how participants recover from these distraction costs over time. As compared to static displays that are often used to measure contingent attentional capture, the dynamic display produces much larger effects, allowing the researcher to identify subtle effects of smaller manipulations. An unusual aspect of our design is that it employs a continuous display; &#34;filler&#34; stimuli connect one trial to the next seamlessly, and participants respond during this interval whenever they detect a target. The continuous display reduces chance performance to near-zero levels (rather than 50%) and provides researchers with a more sensitive measure of performance differences across trial types.

This method uses a dynamic visual display to index costs of distraction during visual search, including both &#34;contingent attentional capture&#34; and &#34;set-specific capture,&#34; which is a cost of distraction that occurs when the participants maintain multiple search goals simultaneously. This method has revealed basic mechanisms and limitations of visual attention.

This method uses a rapid serial visual presentation (RSVP) paradigm to measure the cost of distraction when participants maintain multiple search goals. ...

Using the Visual World Paradigm to Study Sentence Comprehension in Mandarin-Speaking Children with Autism

Sentence comprehension relies on the ability to rapidly integrate different types of linguistic and non-linguistic information. However, there is currently a paucity of research exploring how preschool children with autism understand sentences using different types of cues. The mechanisms underlying sentence comprehension remains largely unclear. The present study presents a protocol to examine the sentence comprehension abilities of preschool children with autism. More specifically, a visual world paradigm of eye-tracking is used to explore the moment-to-moment sentence comprehension in the children. The paradigm has multiple advantages. First, it is sensitive to the time course of sentence comprehension and thus can provide rich information about how sentence comprehension unfolds over time. Second, it requires minimal task and communication demands, so it is ideal for testing children with autism. To further minimize the computational burden of children, the present study measures eye movements that arise as automatic responses to linguistic input rather than measuring eye movements that accompany conscious responses to spoken instructions.

We present a protocol to examine the use of morphological cues during real-time sentence comprehension by children with autism.

Sentence comprehension relies on the ability to rapidly integrate different types of linguistic and non-linguistic information. However, there is ...

Multi-Modal Signals for Analyzing Pain Responses to Thermal and Electrical Stimuli

The assessment of pain relies mostly on methods that require a person to communicate. However, for people with cognitive and verbal impairments, existing methods are not sufficient as they lack reliability and validity. To approach this problem, recent research focuses on an objective pain assessment facilitated by parameters of responses derived from physiology, and video and audio signals. To develop reliable automated pain recognition systems, efforts have been made in creating multimodal databases in order to analyze pain and detect valid pain patterns. While the results are promising, they only focus on discriminating pain or pain intensities versus no pain. In order to advance this, research should also consider the quality and duration of pain as they provide additional valuable information for more advanced pain management. To complement existing databases and the analysis of pain regarding quality and length, this paper proposes a psychophysiological experiment to elicit, measure, and collect valid pain reactions. Participants are subjected to painful stimuli that differ in intensity (low, medium, and high), duration (5 s / 1 min), and modality (heat / electric pain) while audio, video (e.g., facial expressions, body gestures, facial skin temperature), and physiological signals (e.g., electrocardiogram [ECG], skin conductance level [SCL], facial electromyography [EMG], and EMG of M. trapezius) are being recorded. The study consists of a calibration phase to determine a subject&#8217;s individual pain range (from low to intolerable pain) and a stimulation phase in which pain stimuli, depending on the calibrated range, are applied. The obtained data may allow refining, improving, and evaluating automated recognition systems in terms of an objective pain assessment. For further development of such systems and to investigate pain reactions in more detail, additional pain modalities such as pressure, chemical, or cold pain should be included in future studies. Recorded data of this study will be released as the &#8220;X-ITE Pain Database&#8221;.

This article focuses on the experimental elicitation of pain through heat (thermal) and electrical stimulation while recording physiological, visual, and paralinguistic responses. It aims at collecting valid multimodal data for analyzing pain based on its intensity, quality, and duration.&#160;

The assessment of pain relies mostly on methods that require a person to communicate. However, for people with cognitive and verbal impairments, existing ...