The study of inter-trial effects in visual search has generated an increasing amount of research in recent years. However, the mechanisms underlying these effects are still a matter of debate. Two rival accounts have been suggested. One view stipulates that inter-trial effects facilitate early perceptual/attentional processes, whereas the other proposes that it affects post-perceptual response-related processes. Here, we focused on the priming of pop-out effect (PoP, Maljkovic & Nakayama, 1994), which refers to the well-established finding that performance on singleton search is faster when the target and distractors features repeat on two consecutive trials than when they switch. We set out to resolve the current controversy surrounding PoP by suggesting a dual-stage account, according to which PoP speeds both an early perceptual stage and a later, response-related stage of visual search. We were able to dissociate the hypothesized components of PoP by tracking their time course.

Humans often fail to identify a target because of nearby flankers. The nature and stages at which this crowding occurs are unclear, and whether crowding operates via a common mechanism across visual dimensions is unknown. Using a dual-estimation report ( N = 42), we quantitatively assessed the processing of features alone and in conjunction with another feature both within and between dimensions. Under crowding, observers misreported colors and orientations (i.e., reported a flanker value instead of the target’s value) but averaged the target’s and flankers’ spatial frequencies (SFs). Interestingly, whereas orientation and color errors were independent, orientation and SF errors were interdependent. These qualitative differences of errors across dimensions revealed a tight link between crowding and feature binding, which is contingent on the type of feature dimension. These results and a computational model suggest that crowding and misbinding are due to pooling across a joint coding of orientations and SFs but not of colors.

Previous research has shown that intertrial repetition of target and distractors task-relevant properties speeds visual search performance, an effect known as priming of pop-out (PoP). Recent accounts suggest that such priming results, at least in part, from a mechanism that speeds post-selectional, response-related processes, the marker of which is an interaction between repetition of the target and distractor features and repetition of the response from the previous trial. However, this response-based component of inter-trial priming has been elusive, and it remains unclear what its boundary conditions might be. In addition, what information is represented in the episodic memory traces that underlie the response-based component has not yet been characterized. Here, we show that the response-based component of feature priming reflects an episodic memory retrieval mechanism that is not mandatory or automatic but may be described as a heuristic that subjects sometimes use, in particular when the overall difficulty of the search task is high. In addition, we show that the conjunction of the target and distractor features forms the context that is reactivated during episodic retrieval. Finally, we show that target-distractor discriminability is an important modulator of the selection-based component. The findings are discussed within the framework of the dual-stage model of inter-trial priming (Lamy, Yashar, & Ruderman, 2010).

Implicit short-term memory plays an important role in visual search. For instance, singleton search is faster when the target and distractor features repeat on two consecutive trials than when they switch, an effect called Priming of Popout (PoP). However, whether or not PoP facilitates early perceptual/attentional processes remains controversial. To resolve discrepancies between existing findings, we tested the hypothesis that early effects of PoP occur only if attention is focused/engaged on the target. We measured search accuracy using brief displays for a fine discrimination task, which required focused attention, and for a left/right hemifield localization task, which did not. We found that PoP effects on accuracy occur only in the discrimination task. The theoretical implications are discussed.