Grating detection and identification dissociated by pattern adaptation

It two gratings differ in a higher harmonic only, grating identification is expected to depend on that harmonic detection. Yet the comparison of data from several studies suggests that pattern adaptation might differently affect detection and identification. In order to verify this dissociation, a study was made of the effects of adaptation to complex gratings and their harmonics on the detection of the harmonics and on the identification of the complex gratings. Square-wave, first-plus-third-harmonic and missing-fundamental complex gratings were used. The threshold was measured either by the two-interval forced-choice method or by the one-interval method of constant stimuli. For all types of stimuli and procedures, the detection threshold was mostly elevated after adaptation to the corresponding harmonic and the identification threshold was mostly elevated after adaptation to the complex stimulus. This dissociation could only partly be related to the presence of higher harmonics or to the psychophysical procedure. Analysis of threshold changes by adaptation and of phenomenal stimulus appearance suggests that both local features and more global features might contribute to grating identification.