Yukiyasu Kamitani

Illusions. What you see is what you hear.

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.

Visual illusion induced by sound.

We present the first cross-modal modification of visual perception which involves a phenomenological change in the quality-as opposed to a small, gradual, or quantitative change-of the percept of a non-ambiguous visual stimulus. We report a visual illusion which is induced by sound: when a single flash of light is accompanied by multiple auditory beeps, the single flash is perceived as multiple flashes. We present two experiments as well as several observations which establish that this alteration of the visual percept is due to cross-modal perceptual interactions as opposed to cognitive, attentional, or other origins. The results of the second experiment also reveal that the temporal window of these audio-visual interactions is approximately 100 ms.

Manifestation of scotomas created by transcranial magnetic stimulation of human visual cortex

Reduced visual performance under transcranial magnetic stimulation (TMS) of human visual cortex demonstrates suppression whose spatial extent is not directly visible. We created an artificial scotoma (region missing from a visual pattern) to directly visualize the location, size and shape of the TMS-induced suppression by following a large-field, patterned, visual stimulus with a magnetic pulse. The scotoma shifted with coil position according to known topography of visual cortex. Visual suppression resulted in pattern-dependent distortion, and the scotoma was filled in with temporally adjacent stimuli, suggesting spatial and temporal completion mechanisms. Thus, perceptual measurements of TMS-induced suppression may provide information about cortical processing via neuronal connections and temporal interactions of neural signals.

A model of magnetic stimulation of neocortical neurons

Abstract Transcranial magnetic stimulation (TMS) has been widely used in studies of human motor and cognitive functions as well as in clinical treatment. Biophysical mechanism underlying its effect is, however, largely unknown. Here, we develop a theory to calculate the effect of magnetic stimulation on arbitrary neuronal structure. Then, we employ a computer simulation which combines a realistic multicompartmental model of neocortical neurons and the calculation of the induced electric field. The simulation shows that a single magnetic pulse applied to model cortical neurons can induce brief burst firing followed by a silent period of duration comparable to experimental data of TMS. Our simulation offers a new clue to understand physiology of TMS by demonstrating that magnetic stimulation acts on biophysics of the dendrites in neocortical neurons.