Spatial waveform discrimination following higher-harmonic adaptation.
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 3f adaptation has only a negligible effect on discrimination thresholds. In a further experiment, we adapted observers to both 3f and 5f harmonic frequencies of the square-wave test grating presented sequentially over 4 min. Although substantial threshold elevations occurred at the 3f and 5f 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.
Greenlee
M W
MW
Neurologische Universitätsklinik mit Abteilung für Neurophysiologie, Freiburg im Breisgau, Federal Republic of Germany.
Magnussen
S
S
D000222:Adaptation, Physiological; D015350:Contrast Sensitivity; D004056:Differential Threshold; D004192:Discrimination, Psychological; D006801:Humans; D008960:Models, Psychological; D013028:Space Perception / Q000502:physiology*