PERCEPTION OF S-CONE, ML-CONE AND ACHROMATIC CONTRAST BY AWAKE BEHAVING CATS
Recently, we described the temporal characteristics of color-sensitive (blue-ON) cells in the lateral geniculate nucleus (LGN) of anaesthetized cats. Since anatomically, this pathway is heavily underrepresented compared to the achromatic channel, we were wondering (1) if this system plays a role in color vision on the perceptual level and (2) if the sluggish behavior of thalamic blue-ON cells is reflected in reaction times to S-cone isolating stimuli. We trained two male cats to perform a simple contrast discrimination task where they had to respond to the appearance of a spot by pressing a glass plate located in front of the stimulus monitor. We rewarded responses given within a limited time window by liquified food. The target spot had 50% positive or negative cone-contrast for ML-, S- or both cones (achromatic) against the grey background and trials without a target were used as control. We measured simple reaction times (RT) and percentage of correct trials. RTs were not significantly different for the three color conditions (S: 909±214 ms, ML: 906±198 ms, ach: 875±211 ms (mean±SD), p=0.46, ANOVA). Percentage of correct trials was significantly lower for the S-cone isolating condition than for the achromatic one (56±18% and 74±19%, respectively, (mean±SD), p=0.015, ANOVA). Performance for ML-cone isolating stimuli was between that of the other two conditions but did not differ significantly (65±14%, ML vs S: p=0.17, ML vs Ach: p=0.14). We conclude that the S-cone-driven pathway plays an important role in cat color perception but S-cone isolating colors are harder to see.