Cottereau BR

Durand JB

Rima S

Reward seeking shapes our interactions with the environment, but whether it also influences how we perceive it remains controversial. Notably, there is currently a debate on whether objects that are more likely to provide high reward might be perceived bigger than those associated with low reward. The aim of this study is to test this \uab wishful seeing \ubb hypothesis in non-human primates. Two macaque monkeys performed a two-alternative forced choice (2 AFC) size discrimination task during several weeks. Following an initial fixation period, the animals were required to make a saccade towards the biggest of two simultaneously displayed discs, located in diametrically opposite positions relatively to the fixation point (7\ub0 eccentricity). Correct trials were followed by a liquid reward. The disk positions determined the probability of receiving a high versus a low amount of fluid (5/1 ratio). In half of the trials, the 2 discs appeared in positions with equal probability of high reward (neutral conditions, p=0.5/p=0.5) while in the other trials, the probability of high reward was asymmetric (reward-biased conditions, p=0.8/p=0.2). Preliminary results indicate that the saccade latencies are directly related to the probability of getting a high reward (i.e. saccades toward more rewarded positions are significantly shorter that saccades toward less rewarded positions), in agreement with previous reports. Our results also reveal massive differences in the psychometric curves associated with the neutral and reward-biased conditions. Monkeys tend to choose highly rewarded positions irrespective of the sensory evidence, which suggests a reward-induced change in strategy rather than in perception. However, we also observe an interaction between reward probability and sensory evidences that might indicate reward-induced changes in perceived size, in agreement with the wishful seeing hypothesis

"Wishful seeing" in non-human primates: can reward shape size perception?

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