Tuning to non-veridical features in attention and perceptual decision-making

TL;DR

This study investigates how attention is initially tuned to relative features of objects rather than their veridical attributes, and how later decision processes shift towards optimal features, using EEG measures during visual search tasks.

Contribution

It provides evidence that covert attention initially focuses on relative object features, supporting the relational account, with a subsequent bias towards optimal features during decision-making.

Findings

Early attention is tuned to relative features, as shown by N2pc differences.

Later decision-making is biased towards optimal features, affecting accuracy.

Results are consistent across eye-tracking and EEG measures.

Abstract

When searching for a lost item, we tune attention to the known properties of the object. Previously, it was believed that attention is tuned to the veridical attributes of the search target (e.g., orange), or an attribute that is slightly shifted away from irrelevant features towards a value that can more optimally distinguish the target from the distractors (e.g., red-orange; optimal tuning). However, recent studies showed that attention is often tuned to the relative feature of the search target (e.g., redder), so that all items that match the relative features of the target equally attract attention (e.g., all redder items; relational account). Optimal tuning was shown to occur only at a later stage of identifying the target. However, the evidence for this division mainly relied on eye tracking studies that assessed the first eye movements. The present study tested whether this division can also be observed when the task is completed with covert attention and without moving the eyes. We used the N2pc in the EEG of participants to assess covert attention, and found comparable results: Attention was initially tuned to the relative colour of the target, as shown by a significantly larger N2pc to relatively matching distractors than a target-coloured distractor. However, in the response accuracies, a slightly shifted, "optimal" distractor interfered most strongly with target identification. These results confirm that early (covert) attention is tuned to the relative properties of an item, in line with the relational account, while later decision-making processes may be biased to optimal features.