Abstract
Animals exhibit different degrees of preference toward various visual stimuli. In addition, it has been shown that strongly preferred stimuli can often act as a reward. The aim of the present study was to determine what features determine the strength of the preference for visual stimuli in order to examine neural mechanisms of preference judgment. We used 50 color photographs obtained from the Flickr Material Database (FMD) as original stimuli. Four macaque monkeys performed a simple choice task, in which two stimuli selected randomly from among the 50 stimuli were simultaneously presented on a monitor and monkeys were required to choose either stimulus by eye movements. We considered that the monkeys preferred the chosen stimulus if it continued to look at the stimulus for an additional 6 s and calculated a choice ratio for each stimulus. Each monkey exhibited a different choice ratio for each of the original 50 stimuli. They tended to select clear, colorful and in-focus stimuli. Complexity and clarity were stronger determinants of preference than colorfulness. Images that included greater amounts of spatial frequency components were selected more frequently. These results indicate that particular physical features of the stimulus can affect the strength of a monkey’s preference and that the complexity, clarity and colorfulness of the stimulus are important determinants of this preference. Neurophysiological studies would be needed to examine whether these features of visual stimuli produce more activation in neurons that participate in this preference judgment.
Highlights
When humans and non-human primates observe a variety of visual stimuli, they often exhibit different degrees of preference toward these stimuli
These results indicate that, all of the monkeys exhibited a spatial bias in stimulus selection where the strength of the bias varied among the monkeys, stimulus selection during the choice period depended on the preference for the stimuli in at least three monkeys (Monkeys H, M and Y)
An animal’s preference for stimuli or items has been examined using a simple choice task, in which the animal was requested to select one stimulus from among two or more different stimuli presented simultaneously, or by measuring how long or how many times the animal watched a particular stimulus. The strength of this preference can be estimated by the choice ratio for each stimulus, the duration or frequency that the animal watched each stimulus, or how close the animal comes to the stimulus
Summary
When humans and non-human primates observe a variety of visual stimuli, they often exhibit different degrees of preference toward these stimuli. The differences in preference for stimuli often influences choice behavior, such that visually preferred stimuli are behaviorally selected more frequently than others. Behavioral studies using capuchin monkeys and squirrel monkeys have revealed that they more frequently select stimuli with symmetrical and regular patterns compared to stimuli with unsymmetrical and irregular patterns (Anderson et al, 2005). Butler and Woolpy (1963) showed that rhesus monkeys preferred to see colored short movies compared with monochrome movies or photographs. Fujita (1987) presented a variety of images and photographs to five species of macaque monkeys (Macaca fuscata, Macaca mulatta, Macaca radiata, Macaca nemestrina, Macaca arctoides) and found that monkeys preferred watching photographs of the same species. Behavioral studies using capuchin monkeys and squirrel monkeys have revealed that they more frequently select stimuli with symmetrical and regular patterns compared to stimuli with unsymmetrical and irregular patterns (Anderson et al, 2005). Butler and Woolpy (1963) showed that rhesus monkeys preferred to see colored short movies compared with monochrome movies or photographs. Fujita (1987) presented a variety of images and photographs to five species of macaque monkeys (Macaca fuscata, Macaca mulatta, Macaca radiata, Macaca nemestrina, Macaca arctoides) and found that monkeys preferred watching photographs of the same species. Swartz and Rosenblum (1980) obtained
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