measuring-sensitivity-to-viewpoint-change-with-without-stereoscopic

Measuring Sensitivity to Viewpoint Change with and without Stereoscopic Cues

The speed and accuracy of object recognition is compromised by a change in viewpoint; demonstrating that human observers are sensitive to this ...

University of Western Australia

The effects of adaptation to radial and rotational polar optic flow on the classification of noisy test patterns are shown to be very similar to the effects of adaptation to polar Glass patterns on the classification of noisy Glass patterns (Clifford, C. W. G. & Weston, E. (2005). Aftereffect of adaptation to Glass patterns. Vision Research, 45 1355-1363.). In both cases there is a large shift in the signal strength at which test patterns are classified as radial or rotational with equal probability. Two asymmetries were discovered: (1) adaptation to optic flow alters the classification of Glass patterns, but the reverse is not true; and (2) adaptation to Glass patterns decreases detectability of patterns of the same type, but adaptation to optic flow has little effect on the detectability of patterns of any type. We conclude that the mechanisms that detect radial and rotational Glass patterns are independent and independently adaptable, but that the mechanisms that detect the path of optic flow, when directional effects are cancelled out, are linked in an opponent, push-pull fashion.

Effects of adaptation to Glass pattern structure and to path of optic flow.

The retinal flow of information during locomotion provides cues to instantaneous heading. Reconciliation of observer trajectory with the internal representation of the environment implies that the positions of the centre of structure of global motion can be localized relative to points in the visual field. Humans are also sensitive to global structure in Glass patterns, which can approximate temporally integrated optic flow. Encoding of the position of centre of structure of Glass patterns could augment the motion information. However, Glass-like pattern structure could also be present in the texture of objects and indicate their centres, raising the question of whether the centres of form and motion patterns are encoded separately. Psychophysical methods are used to examine ability to localize the centres of structure of Glass and global dot motion (GDM) patterns. Radial and concentric Glass patterns are localized more precisely than spiral Glass patterns but performance in localizing the centres of radial, concentric and spiral GDM patterns is equally precise. Also, Glass patterns centres can be localized at signal levels close to their threshold for discrimination from wholly incoherent patterns but GDM pattern centres cannot, suggesting that detectors for looming and rotating stimuli exist that do not rely on the provision of a centre of structure. Collectively, our results provide evidence for independent encoding of the positions of the centres of structure of global motion and form patterns. These positions can be accurately and precisely localized within the visual field. While the centres of structure of a number of form patterns can be simultaneously encoded, allowing their positions to be compared, only a single focus of expansion for optic flow is returned.

Position encoding of the centres of global structure: separate form and motion processes.

This study aimed to revisit previous findings of superior processing of motion direction in migraineurs with a more stringent direction discrimination task and to investigate whether increased internal noise can account for motion processing deficits in migraineurs.

Edwin Dickinson

School of Psychology

University of Western Australia

Measuring Sensitivity to Viewpoint Change with and without Stereoscopic Cues

Edwin Dickinson

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University of Western Australia

Measuring Sensitivity to Viewpoint Change with and without Stereoscopic Cues

School of Psychology