Interaction of spatial frequency and separation in vernier acuity.
There are two general theories which attempt to explain the ability to judge the relative positions of objects in the visual field. The first is the "local-sign" model which assigns location to individual features of the stimulus. The other is the "channel" model involving pooling of responses of overlapping filters having different spatial frequency and orientation tuning. We set out to investigate these using vernier stimuli whose frequency content could be controlled. The stimuli consisted of vertically orientated sinusoidal gratings placed one above the other with a variable separation between them. Thresholds for high frequency gratings increased rapidly with separation while low frequencies were little affected. In addition the cycle width of gratings which could just be distinguished as being in or out of phase and of gratings which gave optimum vernier acuity both increased linearly with separation. Results are discussed in terms of a model based on spatial frequency filters and we suggest that our findings place significant constraints upon a local-sign model.
Whitaker
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D
Department of Vision Sciences, Aston University, Aston, Triangle, Birmingham, U.K.
MacVeigh
D
D
D015350:Contrast Sensitivity / Q000502:physiology; D003867:Depth Perception / Q000502:physiology*; D006801:Humans; D008297:Male; D008959:Models, Neurological; D010364:Pattern Recognition, Visual / Q000502:physiology; D012684:Sensory Thresholds / Q000502:physiology; D014792:Visual Acuity / Q000502:physiology