Second-order optic flow processing.
Optic flow-large-field rotational and radial motion-is processed as efficiently as translational motion for first-order (luminance-defined) stimuli. However, it has been suggested recently that the same pattern does not hold for second-order (e.g. contrast-defined) stimuli. We used random dot kinematogram (RDK) stimuli to determine whether global processing of optic flow is as efficient as processing of global translational motion for both first- and second-order stimuli. For first-order stimuli, we found that coherence thresholds for radial and rotational motion were equivalent to thresholds for translational motion, supporting previous findings. For second-order stimuli we found, firstly, that given sufficient contrast, second-order optic flow can be processed as efficiently as first-order optic flow and, secondly, that rotational and translational second-order motion are processed with equal efficiency. This contradicts the suggestion that there is a loss of efficiency between integration of second-order global motion and second-order optic flow. The third interesting finding was that the processing of radial second-order motion appears to suffer from a deficit that is dependent upon both the contrast and spatial extent of the stimulus. Further experiments discounted the possibility that the observed deficit is caused by a centrifugal or centripetal bias, but demonstrated that a longer temporal integration period for radial second-order motion is responsible for the observed difference. For durations of approximately 850ms, all three types of motion are processed with equal efficiency.
Aaen-Stockdale
Craig
C
Department of Ophthalmology, McGill Vision Research, McGill University, Royal Victoria Hospital, 687 Pine Ave West, Rm H4-14, Montreal, Que., Canada H3A 1A1.
Ledgeway
Tim
T
Hess
Robert F
RF
D000328:Adult; D015350:Contrast Sensitivity; D003867:Depth Perception; D006801:Humans; D009039:Motion Perception; D010775:Photic Stimulation / Q000379:methods; D011601:Psychophysics; D012399:Rotation; D012684:Sensory Thresholds; D013028:Space Perception; D013997:Time Factors