The pedestal effect of vision on touch

Ehsan Arabzadeh, School of Psychology, University of Sydney

Abstract
In order to construct a coherent percept of the world, our brain continuously combines information across multiple sensory modalities. However, early sensory processing is usually assumed to be unimodal where the activity in one system has little if any influence on another. Early sensory processing is described as a transducer function with a sigmoid shape converting the stimulus into neuronal response. Because of its sigmoid shape, a transducer function exhibits an accelerating nonlinearity at low stimulus values (near detection threshold) and a compressive nonlinearity for higher stimulus values. This feature gives rise to the “pedestal effect” – an improvement in the stimulus detectability when a low baseline value is added to it. We first investigated the pedestal effect within the tactile modality. Using a 2-alternative-forced-choice detection (or discrimination) paradigm, we measured the subjects’ just-noticeable-difference (JND) threshold for vibrations with different amplitudes. Each of the four subjects tested showed an effect of pedestal with the lowest JND thresholds for pedestal values around threshold. We then studied the transfer of the pedestal effect from vision to touch. Results showed that a visual pedestal can in fact facilitate the detection of a tactile vibration.

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