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. 2025 Aug;87(6):1888-1903.
doi: 10.3758/s13414-025-03111-9. Epub 2025 Jun 18.

Ensemble perception requires attention

Ruth Kimchi  1   2 , Shahar Sabary  3
Affiliations

Ensemble perception requires attention

Ruth Kimchi et al. Atten Percept Psychophys. 2025 Aug.

Abstract

The question of whether ensemble perception can take place without attention is unresolved. We examined this issue in four experiments, using an inattention paradigm that provides an on-line, indirect measure of processing of unattended stimuli. Participants performed an attention-demanding change-detection task on a small matrix presented on a background of task-irrelevant ensemble consisting of circles of different size (Experiment 1) or oriented lines (Experiments 2-4). Independently of any change in the matrix, the ensemble mean changed or stayed the same between successive displays on each trial. We hypothesized that if ensemble mean is extracted under inattention, changes in the ensemble mean would produce congruency effects on the speed or accuracy of performance in the matrix change judgments, such that performance is faster or more accurate on congruent than incongruent trials. The results showed that changes in the ensemble mean size or mean orientation produced no congruency effects on performance of the target change-detection task. Also, participants could not report, when probed with surprise questions, whether or not the ensemble mean changed. When participants attended to the ensemble, their accuracy of explicit reports about a change were significantly above chance. These results are seen to suggest that ensemble perception requires attention. The differences between the present study and previous ones, concerning the conditions and definition of unattended and their implication for understanding the relation between ensemble perception and attention, are discussed.

Keywords: Attention; Automatic processing; Ensemble perception; Implicit processing; Unattended processing.

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Conflict of interest statement

Declarations. Ethics approval: The study protocol was approved by the ethics committee of the University of Haifa (437/23). Consent to participate: Written informed consent was obtained from all participants prior to participation. Consent for publication: All participants gave prior informed consent for anonymized data to be used in publications. Conflict of interest: All authors declare that they have no conflicts of interest. Open practices statement: The data of all experiments are available via the Open Science Framework at https://osf.io/p78yu/ . Program code is available upon request.

Figures

Fig. 1
Fig. 1
Examples of the displays presented in Experiments 1–4. Each display consisted of a central target matrix surrounded by an ensemble comprising outline circles of different sizes in Experiment 1 and lines of different orientations in Experiments 2–4. There were two possible means for each ensemble (see text for details). Stimuli are a bit darker in the figure for illustration purposes only
Fig. 2
Fig. 2
Sequence of events in a trial. The illustration depicts two examples of trials: (A) a same-target (central matrix is unchanged) different-ensemble (mean size of the circles changes) trial (from Experiment 1), and (B) a different-target (central matrix changes) same-ensemble (mean orientation of the lines does not change) trial (from Experiment 3)
Fig. 3
Fig. 3
Results of Experiment 1a. Mean correct reaction time (left panel) and accuracy (right panel) for same and different targets as a function of ensemble mean (same, different). Error bars represent within-subjects SEM
Fig. 4
Fig. 4
Results of Experiment 2a. Mean correct reaction time (left panel) and accuracy (right panel) for same and different targets as a function of ensemble mean (same, different). Error bars represent within-subjects SEM
Fig. 5
Fig. 5
Results of Experiment 3a. Mean correct reaction time (left panel) and accuracy (right panel) for same and different targets as a function of ensemble mean orientation (same, different). Error bars represent within-subjects SEM
Fig. 6
Fig. 6
Results of Experiment 4. Mean correct reaction time (left panel) and accuracy (right panel) for same and different targets as a function of ensemble mean orientation (same, different). Error bars represent within-subjects SEM
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