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We can search for and locate specific objects in our environment by looking for objects with similar features. Object recognition involves stimulus similarity responses in ventral visual areas and task-related responses in prefrontal cortex. We tested whether neurons in the lateral intraparietal area (LIP) of posterior parietal cortex could form an intermediary representation, collating information from object-specific similarity map representations to allow general decisions about whether a stimulus matches the object being looked for. We hypothesized that responses to stimuli would correlate with how similar they are to a sample stimulus. When animals compared two peripheral stimuli to a sample at their fovea, the response to the matching stimulus was similar, independent of the sample identity, but the response to the nonmatch depended on how similar it was to the sample: the more similar, the greater the response to the nonmatch stimulus. These results could not be explained by task difficulty or confidence. We propose that LIP uses its known mechanistic properties to integrate incoming visual information, including that from the ventral stream about object identity, to create a dynamic representation that is concise, low dimensional, and task relevant and that signifies the choice priorities in mental matching behavior. NEW & NOTEWORTHY Studies in object recognition have focused on the ventral stream, in which neurons respond as a function of how similar a stimulus is to their preferred stimulus, and on prefrontal cortex, where neurons indicate which stimulus is being looked for. We found that parietal area LIP uses its known mechanistic properties to form an intermediary representation in this process. This creates a perceptual similarity map that can be used to guide decisions in prefrontal areas. [ABSTRACT FROM AUTHOR]

The middle temporal (MT) area has long been established as a cortical area involved in the encoding of motion information and has been thought to do so in retinotopic coordinates. It was previously shown that memory for motion has a spatial component by demonstrating that subjects do significantly worse on a match-to-sample task when the stimuli to be compared were spatially separated. The distance at which performance deteriorated (the critical spatial separation) increased at increasing eccentricities, suggesting that area MT was involved in the process. In this study, we asked whether optimal performance occurred when the stimuli were in the same retinotopic or spatiotopic coordinates. We found that the performance was best when the stimuli appeared in the same location in space rather than the same retinal location, after an eye movement. We also found that the relationship between retinal eccentricity and the critical spatial separation approximated that of area MT, as found previously. We conclude that area MT plays an important role in the memory for motion process and that this is carried out in spatiotopic coordinates. This conclusion supports the hypothesis that MT processing may have a spatiotopic component. [ABSTRACT FROM AUTHOR]