Abstract
Campbell and Robson [J. Physiol. (London) 197, 551 (1968)] proposed that a near-threshold square-wave grating can be distinguished from a sine-wave grating of the same spatial frequency and fundamental amplitude when the channel tuned to the third-harmonic component of the square wave reaches its own threshold. To test this hypothesis, we measured waveform discrimination thresholds with ...
Abstract
Campbell and Robson [J. Physiol. (London) 197, 551 (1968)] proposed that a near-threshold square-wave grating can be distinguished from a sine-wave grating of the same spatial frequency and fundamental amplitude when the channel tuned to the third-harmonic component of the square wave reaches its own threshold. To test this hypothesis, we measured waveform discrimination thresholds with two-interval forced-choice methods before and after 4-min adaptation to a high-contrast sine-wave grating, the spatial frequency of which equaled that of the square wave’s third harmonic. The results indicate that 3ƒ adaptation has only a negligible effect on discrimination thresholds. In a further experiment, we adapted observers to both 3ƒ and 5ƒ harmonic frequencies of the square-wave test grating presented sequentially over 4 min. Although substantial threshold elevations occurred at the 3ƒ and 5ƒ frequencies, the elevation in waveform discrimination threshold was small. These results suggest that the independent-channel hypothesis alone cannot account for the visibility of complex features (edges) following harmonic adaptation.
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