Why the whole is more than the sum of its parts: Salience-driven overestimation in aggregated tactile sensations

Abstract

Experimental psychology often studies perception analytically, reducing its focus to minimal sensory units, such as thresholds or just noticeable differences in a single stimulus. Here, in contrast, we examine a synthetic aspect: how multiple inputs to a sensory system are aggregated into an overall percept. Participants in three experiments judged the total stimulus intensity for simultaneous electrical shocks to two digits. We tested whether the integration of component somatosensory stimuli into a total percept occurs automatically, or rather depends on the ability to consciously perceive discrepancy among components (Experiment 1), whether the discrepancy among these components influences sensitivity or/and perceptual bias in judging totals (Experiment 2), and whether the salience of each individual component stimulus affects perception of total intensity (Experiment 3). Perceptual aggregation of two simultaneous component events occurred both when participants could perceptually discriminate the two intensities, and also when they could not. Further, the actual discrepancy between the stimuli modulated both participants’ sensitivity and perceptual bias: increasing discrepancies produced a systematic and progressive overestimation of total intensity. The degree of this bias depended primarily on the salience of the stronger stimulus in the pair. Overall, our results suggest that important nonlinear mechanisms contribute to sensory aggregation. The mind aggregates component inputs into a coherent and synthetic perceptual experience in a salience-weighted fashion that is not based on simple summation of inputs.

Somatosensory evoked potentials that index lateral inhibition are modulated according to the mode of perceptual processing: comparing or combining multi-digit tactile motion

“…The difference in performance was significant (paired-sample t-test: t 14 = 3.5, p = .004, d = .90). Previous studies have also found that somatosensory aggregation tends to produce better performance than discrimination (Cataldo et al, 2019), possibly reflecting that the aggregate can be derived even when discrepancy between stimuli is unclear. Performance between the tasks was not correlated across participants (r = .20, p = .47), showing no evidence for a common computational factor underlying individual differences in performance.…”

“…The ability to extract overall or average motion information from multiple, simultaneous motion cues has been described in vision (Watamaniuk & McKee, 1998;Watamaniuk et al, 1989) under the idea of ensemble perception (for review see Alvarez, 2011;Whitney & Yamanashi Leib, 2018). In touch, a few studies have investigated aggregation of tactile features such as intensity or frequency (Cataldo et al, 2019;Kuroki et al, 2017;Walsh et al, 2016). However, when an object held between fingers begins to move, the overall motion direction of the object can be also clearly perceived (Martin, 1992).…”

Somatosensory evoked potentials, indexing lateral inhibition, are modulated according to the mode of perceptual processing: comparing or combining multi-digit tactile motion

“…The difference in performance was significant (paired-sample t-test: t 14 = 3.5, p = .004, d = .90). Previous studies have also found that somatosensory aggregation tends to produce better performance than discrimination (Cataldo et al, 2019), possibly reflecting that the aggregate can be derived even when discrepancy between stimuli is unclear. Performance between the tasks was not correlated across participants (r = .20, p = .47), showing no evidence for a common computational factor underlying individual differences in performance of both averaging and discrimination tasks.…”

“…The ability to extract overall or average motion information from multiple, simultaneous motion cues has been described in vision (Watamaniuk et al, 1989;Watamaniuk and McKee, 1998) under the idea of ensemble perception (for review see Alvarez, 2011;Whitney and Yamanashi Leib, 2018). In touch, a few studies have investigated aggregation of tactile features such as intensity or frequency (Walsh et al, 2016;Kuroki et al, 2016;Cataldo et al, 2019). However, when an object held between fingers begins to move, the overall motion direction of the object can be also clearly perceived (Martin, 1992).…”

Sensory and cognitive factors affecting multi-digit touch: a perceptual and modeling study

“…Previous studies (Walsh et al, 2016;Cataldo et al, 2019) have also revealed that stimuli delivered to multiple fingers of the same hand are often integrated with unequal sensory weights, but not when they are delivered to two fingers on opposite hands. Capacity limitation in general enforces us to allocate available resources to more relevant stimuli.…”