Preference of Negative Contrast in Behaving Rats
36.4002, Sunday, 17-May, 2:45 pm - 6:45 pm, Pavilion
Sheng-Hui Wu1, Chun-I Yeh1,2; 1Graduate Institutes of Brain and Mind Sciences, College of Medicine, National Taiwan University, 2Department of Psychology, College of Science, National Taiwan University
Humans can detect negative contrast (black on gray) better and more easily than positive contrast (white on gray). The black-over-white preference in visual perception is accordance with the findings that negative-contrast stimuli can evoke larger neuronal responses than positive-contrast stimuli in primary visual cortex (V1) (Zemon et al., 1988; Olmen et al., 2008; Yeh et al., 2009; Xing et al., 2010). In contrast, strong white-dominant responses were recently found in rodent V1 with the voltage-sensitive dye (VSD) imaging technique (Polack & Contreras, 2012). Based on these findings, it is possible that rodents may prefer positive contrast to negative contrast. Here we used a two-alternative forced choice task to test the contrast preference in behaving rodents (Long Evans). We manipulated both the contrast (0%, 8%, 16%, 32%, 64%, 100%) and the mean luminance of the screen (high: 50 cd/m2, low: 20 cd/m2). Surprisingly, we found that rats can detect negative-contrast stimuli better than positive-contrast stimuli. The black-over-white bias is the largest at 100% contrast with the low mean luminance level (the mean difference of the correct rate is 12.27%, SE=2.94%, p=0.0013). On the other hand, rats on average had better performances in the high mean luminance condition than in the low mean luminance. The discrepancy between behavioral and neuronal results in rodents may be due to (1) the difference in the mean luminance (neuronal: 83 cd/m2; behavioral: 20 and 50 cd/m2) and (2) the duration of the stimuli (neuronal: 250 ms; behavioral: on until rats make a choice). Overall, our behavioral results show that rodents can detect negative contrast better than positive contrast. Future studies need to address the contradiction between the behavioral (negative-contrast preferences) and the neuronal (white-dominant responses in V1) results in rodents.