Low attention impairs optimal incorporation of prior knowledge in perceptual decisions

Abstract

When visual attention is directed away from a stimulus, neural processing is weak and strength and precision of sensory data decreases. From a computational perspective, in such situations observers should give more weight to prior expectations in order to behave optimally during a discrimination task. Here we test a signal detection theoretic model that counter-intuitively predicts subjects will do just the opposite in a discrimination task with two stimuli, one attended and one unattended: when subjects are probed to discriminate the unattended stimulus, they rely less on prior information about the probed stimulus' identity. The model is in part inspired by recent findings that attention reduces trial-by-trial variability of the neuronal population response and that they use a common criterion for attended and unattended trials. In five different visual discrimination experiments, when attention was directed away from the target stimulus, subjects did not adjust their response bias in reaction to a change in stimulus presentation frequency despite being fully informed and despite the presence of performance feedback and monetary and social incentives. This indicates that subjects did not rely more on the priors under conditions of inattention as would be predicted by a Bayes-optimal observer model. These results inform and constrain future models of Bayesian inference in the human brain.

Humans incorporate attention-dependent uncertainty into perceptual decisions and confidence

“…Our findings of flexible decision boundaries run counter to a previous proposal that observers use a fixed decision rule under varying attentional conditions [13][14][15]18 . This idea originated from a more general "unified criterion" proposal 22,23 , which asserts that in a display with multiple stimuli, observers adopt a single, fixed decision boundary (the "unified criterion") for all items [19][20][21][22][23][24] .…”

“…Note that observers could take uncertainty into account in other ways, but here we began with a normative approach by using a Bayesian model. In the Fixed model, observers use the same decision criteria, regardless of the attention condition 13,15,[18][19][20][21][22][23][24] (i.e., they are fixed in measurement space, Figure 3a,b). We used Markov Chain Monte Carlo sampling to fit the models to raw, trial-to-trial category and confidence responses from each observer separately (Methods , Table S1).…”

“…Although the unified criterion proposal has served as a parsimonious explanation for experimental findings [13][14][15][18][19][20][21][22][23][24] , it is impossible to infer decision boundaries from behavior in the signal detection theory (SDT) tasks used previously 31 . In theory, it is always possible to explain behavioral data from such tasks with a fixed decision rule, as long as the means and variances of the internal measurement distributions are free to vary (Supplementary Text Section S1).…”

The influence of evidence volatility on choice, reaction time and confidence in a perceptual decision

“…However, characterization of these effects of TMS and µStim was inferred from behavior. Similarly, psychophysical studies that attempted to increase the noise through changes in the visual stimulus (de Gardelle and Summerfield, 2011; Zylberberg et al, 2014; de Gardelle and Mamassian, 2015) or attentional state (Rahnev et al, 2011; Morales et al, 2015) did not characterize the influence of these manipulations on the neural signals that the brain accumulates to form a decision.…”

Perceptual decisions are biased toward relevant prior choices

“…Overall, serialdependence, like predictions more generally, reflects a trade-off between efficiency (relying on biased expectations) and accuracy (relying on instantaneous sensory information).The specific conditions that give rise to serial-dependence are not fully understood. Many factors may trigger it, including sensory inputs Cicchini et al, 2017), motor responses Pape and Siegel, 2016), expectations (Chalk et al, 2010;Kok et al, 2013) and spatial attention Morales et al, 2015). It has even been proposed that prior choices, in and of themselves, can elicit serial-dependence (Kaneko and Sakai, 2015;Talluri et al, 2018).…”