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.