Datensatz

Zusammenfassung

1.How do monkeys classify parameterized visual stimuli in comparison to humans? 2.Which models best describe the classification probabilities? 3.How are the parameterized stimuli represented in the subjects’ psychological space? 4.Are the psychological representations necessary to explain the classification performance? The first set of stimuli consisted of 34 line drawings of Brunswik faces varying along four dimensions: the height of the eyes (EH), the separation of the eyes (ES), the length of the nose (NL) and the height of the mouth (MH). The second set of stimuli consisted of 20 line drawings of fish also varying along four dimensions: the shape of the dorsal fin (DF), the shape of the tail (T), the shape of the ventral fin (VF) and the shape of the mouth (M). The subjects (6 humans and 3 monkeys) first learned two classes of exemplars for each stimulus set and then assigned new exemplars to these two classes in an unsupervised manner. During a second task they rated the similarity of all the stimuli presented in triads. This data was used to derive distances between the stimuli and to determine the psychological representation of the stimuli using Multidimensional Scaling (MDS). The results of the classification task were combined with psychological and parametric stimulus representations to assess the performance of four broad classes of models: exemplar based models, prototype models, cue validity models and linear boundary models. 1.Monkeys classify parameterized visual stimuli similarly to humans. 2.The exemplar based models and the linear boundary models seem to describe best the classification probabilities both for monkeys and humans. 3.The four varying dimensions of the stimuli are not represented uniformly neither in the monkeys’ nor in the humans’ psychological space. Specifically, two dimensions of the schematic faces (EH, ES), and three dimensions of the schematic fish (M, DF, T) were more strongly correlated with the reported similarities than the other dimensions of the stimulus sets. 4.The psychological distances derived from the subjects’ similarity ratings do not improve substantially the fit of the classification models. We established that monkeys classify and represent the visual parameterized stimuli studied here like humans do. Exemplar based models and linear boundary models best describe the classification data both for monkeys and humans. However it is not evident that the psychological distances are necessary in addition to the parametric distances to explain the classification data. The similarity of classification performance in the two species promise interesting insights in the neural mechanism of recognition in primates.