Perception Beyond Gestalt by Geremek Adam; Greenlee Mark; Magnussen Svein

Author:Geremek, Adam; Greenlee, Mark; Magnussen, Svein
Language: eng
Format: epub
Publisher: Taylor and Francis

In a similar fashion, we showed in a subsequent study that higher-harmonic adaptation did not have the expected effect on spatial waveform discrimination (Greenlee and Magnussen, 1988). The contrast required by observers to discriminate between a sinewave and square-wave grating did not increase after adaptation to the harmonic components of the square-wave. Taken together, the results from these two studies placed the independent-channel Fourier theory of pattern detection and waveform discrimination in question. Changes in the sensitivity to harmonic components were evident for simple sinewave test gratings, but these adaptation effects did not alter detection and discrimination thresholds for complex (square-wave) gratings. These differences occurred despite randomized presentation of the waveform patterns and forced-choice techniques. We suggested at the time that these results serve a blow to theories that rely on linear combinations of activities in independent spatial-frequency channels for detection and discrimination of periodic patterns. We proposed that the local features of the patterns that result from combinations of sinewave components with different spatial phases and contrast (i.e. edge detection) needed to be taken into account to be able to predict sensitivity to square-wave patterns after harmonic adaptation.

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