The perception of a briefly presented shape is strongly impaired when it is followed by another pattern, a phenomenon called backward masking. We found that the vast majority of a sample of shape-selective neurons in the macaque inferior temporal cortex respond selectively to backward-masked shapes, although these shapes could not be discriminated by human and monkey subjects. However, this selective response was brief, since it was either interrupted by the mask or overridden by a response to the mask itself. We show that reliable discrimination of briefly presented shapes by single neurons depends on the temporal integration of the response. Presentation of the mask, however, reduces the number of spikes available for integration, explaining backward masking. These results also provide direct neurophysiological evidence for the "interruption theory" of backward masking.