Perceptual learning is the improvement in perceptual performance through training or exposure. Here, we used fMRI before and after extensive behavioral training to investigate the effects of perceptual learning on the recognition of objects under challenging viewing conditions. Objects belonged either to trained or untrained categories. Trained categories were further subdivided into trained and untrained exemplars and were coupled with high or low monetary rewards during training. After a 3-day training, object recognition was markedly improved. Although there was a considerable transfer of learning to untrained exemplars within categories, an enhancing effect of reward reinforcement was specific to trained exemplars. fMRI showed that hippocampus responses to both trained and untrained exemplars of trained categories were enhanced by perceptual learning and correlated with the effect of reward reinforcement. Our results suggest a key role of hippocampus in object recognition after perceptual learning.

When the same visual input has conflicting interpretations, conscious perception can alternate spontaneously between each competing percept. Surprisingly, such bistable perception can be stabilized by intermittent stimulus removal, suggesting the existence of perceptual “memory” across interruptions in stimulation. The neural basis of such a process remains unknown. Here, we studied binocular rivalry, one type of bistable perception, in two linked experiments in human participants. First, we showed, in a behavioral experiment using binocular rivalry between face and grating stimuli, that the stabilizing effect of stimulus removal was specific to perceptual alternations evoked by rivalry, and did not occur following physical alternations in the absence of rivalry. We then used functional magnetic resonance imaging to measure brain activity in a variable delay period of stimulus removal. Activity in the fusiform face area during the delay period following removal of rivalrous stimuli was greater following face than grating perception, whereas such a difference was absent during removal of non-rivalrous stimuli. Moreover, activity in areas of fronto-parietal regions during the delay period correlated with the degree to which individual participants tended to experience percept stabilization. Our findings suggest that percept-related activity in specialized extrastriate visual areas help to stabilize perception during perceptual conflict, and that high-level mechanisms may determine the influence of such signals on conscious perception.

Face and voice processing contribute to person recognition, but it remains unclear how the segregated specialized cortical modules interact. Using functional neuroimaging, we observed cross-modal responses to voices of familiar persons in the fusiform face area, as localized separately using visual stimuli. Voices of familiar persons only activated the face area during a task that emphasized speaker recognition over recognition of verbal content. Analyses of functional connectivity between cortical territories show that the fusiform face region is coupled with the superior temporal sulcus voice region during familiar speaker recognition, but not with any of the other cortical regions normally active in person recognition or in other tasks involving voices. These findings are relevant for models of the cognitive processes and neural circuitry involved in speaker recognition. They reveal that in the context of speaker recognition, the assessment of person familiarity does not necessarily engage supra-modal cortical substrates but can result from the direct sharing of information between auditory voice and visual face regions.