Effects of invisible flankers on invisible adaptor

Abstract

The strength of early adaptation was shown to be reduced by binocular suppression and crowding [Blake et al, 2006 Proceedings of the National Academy of Sciences of the USA 103(12) 4783–4788]. Such reduction was explained as the effects of visual awareness on adaptation. Here we investigated whether flankers could further weaken adaptation when stimuli were rendered perceptually invisible by continuous flash suppression. Four normally sighted observers viewed an adapting grating (4×contrast threshold; 2.5° diameter; 2 cpd) presented to the upper visual field of their non-dominant eye at 10° eccentricity for 5 s. The adaptor was surrounded by four high contrast flankers (8×contrast threshold; 2.7° center-to-center distance) in the crowded conditions. Perceptual visibility of the adaptor (and flankers) was modulated by presenting dynamic noise to their dominant eye. Contrast thresholds for two-interval-forced-choice detection were measured with test gratings in same or orthogonal orientation. The strength of orientation-specific threshold-elevation aftereffect was reduced when the adaptor was flanked. More importantly, attenuated effect of flankers was observed even when both the adaptor and flankers were suppressed from awareness. Flanker interference reduced the strength of early adaptation, regardless of visual awareness. Such interference on neural activity early in visual processing at the site of adaptation was likely to be a bottom-up phenomenon.