Immobility of some second-order stimuli in human peripheral vision.

Real-world objects and events are often demarcated and defined by changes of luminance. Such stimuli are easily noticed by human beings whether the stimuli occur in central or in peripheral vision. It is also possible to use differences of color, texture, contrast, or temporal characteristics to create visual stimuli (so-called non-luminance-domain or second-order stimuli). Here I report the discovery that a variety of spatially periodic, second-order patterns, when set in motion in peripheral vision, appear stationary even though their structure is clearly visible. The immobility of the second-order stimuli is evidenced by the striking inability of observers to report their direction of motion. Special signal transformations are required to reveal the motion of second-order stimuli to higher-stage motion mechanisms, and the immobility of second-order stimuli in peripheral but not in central vision suggests that the processing of the transformed signals by higher-stage motion mechanisms changes radically from central to peripheral vision.