The L/M-Opponent Channel Provides a Distinct and Time-Dependent Contribution towards Visual Recognition

Abstract

The visual pathway has been successfully modelled as containing separate channels consisting of one achromatically opponent mechanism and two chromatically opponent mechanisms. However, little is known about how time affects the processing of chromatic information. Parametrically defined objects were generated. Reduced colour objects were interleaved with full-colour objects and measures of recognition performance (d-prime [d']) were compared using the continuous serial recognition paradigm. Measures were taken at multiple delay intervals (1 s, 4 s, 7 s, and 10 s). When chromatic variations were removed, recognition performance was impaired, but at the 1 s and 10 s intervals only. When luminance variations were removed, no impairment resulted. When only L/Mopponent modulations were removed, a deficit in performance was produced only at the 1 s and 10 s intervals, similar to the removal of chromatic variation. When only Sopponent modulations were removed, no impairment was observed. The results suggest that the L/M-opponent pathway provides a specialized contribution to visual recognition, but that its effect is modulated by time. A three-stage process model is proposed to explain the data. We wanted to examine whether constraints placed on a single dimension (colour) modulated VSTM performance. Understanding VSTM and its role in recognition ability is important as it has the potential to aid normal and deficient behaviour. In this study, the contribution of colour to human visual recognition performance was examined to ascertain the effect of time on removing variation from object stimuli along one or two dimensions of the 3D colour space. The visual pathway has been successfully modelled as containing separate channels consisting of one achromatically opponent mechanism and two chromatically opponent mechanisms (Buchsbaum and Gottschalk 1983). Empirical evidence shows that contrast sensitivity functions for stimuli containing achromatic, L/M-opponent and S-opponent modulations take differing forms, reflecting differences in the properties of the mechanisms that convey each class of signal (Mullen 1985). Adapting stimuli that isolate one of the opponent mechanisms do not alter visual threshold measurements taken along the orthogonal opponent direction (Bradley et al 1988;Krauskopf and Gegenfurtner 1992;Krauskopf et al 1982).Differences in performance have been observed in shape discrimination tasks, measuring the radial modulation threshold for discrimination between circular and non-circular stimuli matched in multiples of stimulus detection threshold. The Sopponent system was found to perform worst, followed by the L/M-opponent system and the achromatic system (Mullen and Beaudot 2002).Imaging studies using functional magnetic resonance imaging (fMRI) have shown how extremely sensitive the visual system is to chromatic modulations of low In this study, we examined how time affects the relative contribution of the L/M-opponent and S-opponent modulations to visual recognition. We were interested in the d...