Contextual influences on a spatial-frequency-contingent color aftereffect.

Abstract

Spatia}:.frequen cy-eontin~nt color aftereffects were induced in eight observers in order to examine the role of apparent spatial frequency in the aftereffects. Test stimuli consisted of ach­ romatic gratings presented either with or without the context of a receding pictorial corridor array. A neutral-point procedure was used to assess the strength of the color aftereffects. The results indicated that both retinal and apparent spatial frequency affected the color aftereffects on those test gratings presented in the context of the corridor array. However, the color after­ effects on the test gratings presented without context were affected only by variationsin retinal spatial frequency. It is concluded that the stimulus for the color aftereffects is not simply the retinal representation of the test stimulus. Therefore, any description of contingent color after­ effects based on selective chromatic adaptation of retinotopically organized cortical feature de­ tectors is not complete. Jordan and Uhlarik (1982) recently reported a color aftereffect contingent on the apparent spatial frequency of test gratings. Subsequent to the induc­ tion of color aftereffects, apparent spatial frequency was varied in one instance by placing test gratings of identical retinal spatial frequency in the context of a receding pictorial array (see Figure 1). A test grat­ ing in the upper region of this array should appear larger (i.e., to have a lower spatial frequency) than the same grating in the lower region of the array due to implicit depth cues and Emmert's law. Question­ naire responses indicated that the saturation and hue of color aftereffects were contingent on the similar­ ity of the apparent spatial frequency of the test grat­ ing to that of the adapting grating: the closer the match between apparent test-grating frequency and the adapting frequency, the more saturated the after­ effect hue. Other investigators have reported color aftereffects contingent on perceptual organization (Uhlarik, Pringle, & Brigell, 1977) and apparent ori­ entation (Mikaelian, 1976) of test gratings. All of these findings are inconsistent with previous observa­ tions that aftereffect strength is greatest when the physical parameters of a test grating match those of the adapting grating. For example, Harris (1970) re­ ported that color aftereffects were contingent on ret