A feature-tracking model simulates the motion direction bias induced by phase congruency,J Vis, 3 (6), 179-195.

Here we report a new motion illusion where the prevailing motion direction is strongly influenced by the relative phase of the harmonic components of the stimulus. The basic stimulus is the sum of three sinusoidal contrast-reversing gratings: the first, the third, and the fifth harmonic of two square wave gratings that drift in opposite direction. The phase of one of the fifth components was kept constant at 180 deg, whereas the phase of the other fifth harmonic was varied over the range 0-150 deg. For each phase value of the fifth harmonic, the motion was strongly biased toward its direction, corresponding to the direction with stronger phase congruency between the three harmonics. The strength of the prevailing motion was assessed by measuring motion direction discrimination thresholds, by varying the contrast of the third and the fifth harmonics plaid pattern. Results show that the contrast of high harmonics had to be increased by more than a factor of 10, to achieve a balance of motion for phase differences greater than 60 deg between the 2 fifth harmonics. We also measured the dependence on the absolute phase of harmonic components and found that it is not an important parameter, excluding the possibility that local luminance cues could be mediating the effect. A feature-tracking model based on previous work is proposed to simulate the data. The model computes local energy function from a pair of space-time separable front stage filters and applies a battery of directional second stage mechanisms. It is able to simulate quantitatively the phase congruency dependence illusion and the insensitivity to overall phase. Other energy models based on directional filters fail to simulate the phase congruency dependency effect.

Development of saccadic suppression in children,J Neurophysiol, 3 (96), 1011-1017.

We measured saccadic suppression in adolescent children and young adults using spatially curtailed low spatial frequency stimuli. For both groups, sensitivity for color-modulated stimuli was unchanged during saccades. Sensitivity for luminance-modulated stimuli was greatly reduced during saccades in both groups but far more for adolescents than for young adults. Adults’ suppression was on average a factor of about 3, whereas that for the adolescent group was closer to a factor of 10. The specificity of the suppression to luminance-modulated stimuli excludes generic explanations such as task difficulty and attention. We suggest that the enhanced suppression in adolescents results from the immaturity of the ocular-motor system at that age.

Perception: transient disruptions to neural space-time,Curr Biol, 19 (16), R847-849.

How vision operates efficiently in the face of continuous shifts of gaze remains poorly understood. Recent studies show that saccades cause dramatic, but transient, changes in the spatial and also temporal tuning of cells in many visual areas, which may underly the perceptual compression of space and time, and serve to counteract the effects of the saccades and maintain visual stability.

Resolution for spatial segregation and spatial localization by motion signals,Vision Res, 6-7 (46), 932-939.

We investigated two types of spatial resolution for perceiving motion-defined contours: grating acuity, the capacity to discriminate alternating stripes of opposed motion from transparent bi-directional motion; and alignment acuity, the capacity to localize the position of motion-defined edges with respect to stationary markers. For both tasks the stimuli were random noise patterns, low-pass filtered in the spatial dimension parallel to the motion. Both grating and alignment resolution varied systematically with spatial frequency cutoff and speed. Best performance for grating resolution was about 10 c/deg (for unfiltered patterns moving at 1-4 deg/s), corresponding to a stripe resolution of about 3′. Grating resolution corresponds well to estimates of smallest receptive field size of motion units under these conditions, suggesting that opposing signals from units with small receptive fields (probably located in V1) are contrasted efficiently to define edges. Alignment resolution was about 2′ at best, under similar conditions. Whereas alignment judgment based on luminance-defined edges is typically 3-10 times better than resolution, alignment based on motion-defined edges is only 1.1-1.5 times better, suggesting motion contours are less effectively encoded than luminance contours.

Separate attentional resources for vision and audition,Proc Biol Sci, 1592 (273), 1339-1345.

Current models of attention, typically claim that vision and audition are limited by a common attentional resource which means that visual performance should be adversely affected by a concurrent auditory task and vice versa. Here, we test this implication by measuring auditory (pitch) and visual (contrast) thresholds in conjunction with cross-modal secondary tasks and find that no such interference occurs. Visual contrast discrimination thresholds were unaffected by a concurrent chord or pitch discrimination, and pitch-discrimination thresholds were virtually unaffected by a concurrent visual search or contrast discrimination task. However, if the dual tasks were presented within the same modality, thresholds were raised by a factor of between two (for visual discrimination) and four (for auditory discrimination). These results suggest that at least for low-level tasks such as discriminations of pitch and contrast, each sensory modality is under separate attentional control, rather than being limited by a supramodal attentional resource. This has implications for current theories of attention as well as for the use of multi-sensory media for efficient informational transmission.

Time perception: space-time in the brain,Curr Biol, 5 (16), R171-173.