Expectation-based blindness: Predictions about object categories gate awareness of focally attended objects

Attention and feature binding in the temporal domain

Previous studies have shown that illusory conjunction can emerge for both spatially and temporally proximal objects. However, the mechanisms involved in binding in the temporal domain are not yet fully understood. In the current study, we investigated the role of attentional processes in correct and incorrect temporal binding, and specifically how feature binding is affected by the speed of attentional engagement. In two experiments, participants searched for a target in a rapid serial visual presentation stream and reported its colour and alphanumeric identity. Temporal binding errors were frequent. Critically, when participants reported the identity of a distractor instead of a target, they were also more likely to report the colour of this distractor. This association was observed both within and between individuals. These findings suggest that attentional engagement facilitates the binding of temporally co-occurring features. We discuss these results within a 'diachronic' framework of selective attention, and also consider other factors that contribute to temporal binding errors.

A dissociation between the effects of expectations and attention in selective visual processing

It is often claimed that probabilistic expectations affect visual perception directly, without mediation by selective attention. However, these claims have been disputed, as effects of expectation and attention are notoriously hard to dissociate experimentally. In this study, we used a new approach to separate expectations from attention. In four experiments (N = 60), participants searched for a target in a rapid serial visual presentation (RSVP) stream and had to identify a digit or a letter defined by a low-level cue (colour or shape). Expectations about the target's alphanumeric category were probabilistically manipulated. Since category membership is a high-level feature and since the target was embedded among many distractors that shared its category, targets from the expected category should not attract attention more than targets from the unexpected category. In the first experiment, these targets were more likely to be identified relative to targets from the unexpected category. Importantly, in the following experiments, we also included behavioural and electrophysiological indices of attentional guidance and engagement. This allowed us to examine whether expectations also modulated these or earlier attentional processes. Results showed that category-based expectations had no modulatory effects on attention, and only affected processing at later encoding-related stages. Alternative interpretation of expectation effects in terms of repetition priming or response bias were also ruled out. These observations provide new evidence for direct attention-independent expectation effects on perception. We suggest that expectations can adjust the threshold required for encoding expectations-congruent information, thereby affecting the speed with which target objects are encoded in working memory.

Attribute amnesia as a product of experience-dependent encoding

Attribute amnesia, a phenomenon in which participants fail to report a just-attended attribute in a surprise test, reflects the importance of expectation in determining memory for attended information. To investigate how expectations arise in the context of attribute amnesia, the present study examined whether and how different response histories, independently of task instruction, can shape expectation, thereby driving or eliminating attribute amnesia. Participants were assigned to three groups and completed variations of the attribute amnesia task, where they were initially instructed to encode both target location and identity. Two groups of participants were probed four times on target identity before a critical identity probe, in one case intermittently while in the other case repeatedly during the first few trials. Another group of participants was never probed on identity until the critical trial, which occurred on the 370th trial (after many location probes). The results showed that, in spite of common task instruction, performance on the critical trial depended strongly on response history, with initial identity probes providing some protection against attribute amnesia and intermittent probes completely eliminating it. The findings suggest that the encoding of information into working memory is determined by task experience, independently of task instruction.

Good-enough attentional guidance

Theories of attention posit that attentional guidance operates on information held in a target template within memory. The template is often thought to contain veridical target features, akin to a photograph, and to guide attention to objects that match the exact target features. However, recent evidence suggests that attentional guidance is highly flexible and often guided by non-veridical features, a subset of features, or only associated features. We integrate these findings and propose that attentional guidance maximizes search efficiency based on a 'good-enough' principle to rapidly localize candidate target objects. Candidates are then serially interrogated to make target-match decisions using more precise information. We suggest that good-enough guidance optimizes the speed-accuracy-effort trade-offs inherent in each stage of visual search.