International Journal of Comparative Psychology

Data are presented showing that humans and non-humans are severely limited in their ability to identify stimuli that vary along a single dimension. Increasing the dimensionality of spatially undifferentiated stimuli improves performance. However, this improvement is trivial compared to that observed when spatially complex stimuli, such as pictures, are presented for identification. The theoretical account of memory and decision processes presented here suggests that, while the number of items that can be held in working memory varies among species, the number of items that can be identified depends more upon the characteristics of the stimuli than upon the organism making the identification.