Salience-driven overestimation of total somatosensory stimulation.

Psychological characterisation of sensory systems often focusses on minimal units of perception, such as thresholds, acuity, selectivity and precision. Research on how these units are aggregated to create integrated, synthetic experiences is rarer. We investigated mechanisms of somatosensory integration by asking volunteers to judge the total intensity of stimuli delivered to two fingers simultaneously. Across four experiments, covering physiological pathways for tactile, cold and warm stimuli, we found that judgements of total intensity were particularly poor when the two simultaneous stimuli had different intensities. Total intensity of discrepant stimuli was systematically overestimated. This bias was absent when the two stimulated digits were on different hands. Taken together, our results showed that the weaker stimulus of a discrepant pair was not extinguished, but contributed less to the perception of the total than the stronger stimulus. Thus, perception of somatosensory totals is biased towards the most salient element. 'Peak' biases in human judgements are well-known, particularly in affective experience. We show that a similar mechanism also influences sensory experience.