Stimulus modality

Abstract: Primary visual cortex receives visual input from the eyes through the lateral geniculate nuclei, but is not known to receive input from other sensory modalities. Its level of activity, both at rest and during auditory or tactile tasks, is higher in blind subjects than in normal controls, suggesting that it can subserve nonvisual functions; however, a direct effect of non-visual tasks on activation has not been demonstrated. To determine whether the visual cortex receives input from the somatosensory system we used positron emission tomography (PET) to measure activation during tactile discrimination tasks in normal subjects and in Braille readers blinded in early life. Blind subjects showed activation of primary and secondary visual cortical areas during tactile tasks, whereas normal controls showed deactivation. A simple tactile stimulus that did not require discrimination produced no activation of visual areas in either group. Thus in blind subjects, cortical areas normally reserved for vision may be activated by other sensory modalities.

Abstract: A computational model is described in which the sizes of variables are represented by the explicit times at which action potentials occur, rather than by the more usual 'firing rate' of neurons. The comparison of patterns over sets of analogue variables is done by a network using different delays for different information paths. This mode of computation explains how one scheme of neuroarchitecture can be used for very different sensory modalities and seemingly different computations. The oscillations and anatomy of the mammalian olfactory systems have a simple interpretation in terms of this representation, and relate to processing in the auditory system. Single-electrode recording would not detect such neural computing. Recognition 'units' in this style respond more like radial basis function units than elementary sigmoid units.

Abstract: Vision is believed to dominate our multisensory perception of the world. Here we overturn this established view by showing that auditory information can qualitatively alter the perception of an unambiguous visual stimulus to create a striking visual illusion. Our findings indicate that visual perception can be manipulated by other sensory modalities.