The Architecture of Object-Based Attention

The object as the unit for state switching in visual working memory

This study aimed to determine the unit for switching representational states in visual working memory (VWM). Two opposing hypotheses were investigated: (a) the unit of switching being a feature (feature-based hypothesis), and (b) the unit of switching being an object (object-based hypothesis). Participants (N = 180) were instructed to hold two features from either one or two objects in their VWM. The memory-driven attentional capture effect, suggesting that actively held information in VWM can cause attention to be drawn towards matched distractors, was employed to assess representational states of the first and second probed colors (indicated by a retro-cue). The results showed that only the feature indicated to be probed first could elicit memory related capture for the condition of separate objects. Importantly, features from an integrated object could guide attention regardless of the probe order. These findings were observed across three experiments involving features of different dimensions, same dimensions, or perceptual objects defined by Gestalt principles. They provide convergent evidence supporting the object-based hypothesis by indicating that features within a single object cannot exist in different states.

Representational structures as a unifying framework for attention

Our visual system consciously processes only a subset of the incoming information. Selective attention allows us to prioritize relevant inputs, and can be allocated to features, locations, and objects. Recent advances in feature-based attention suggest that several selection principles are shared across these domains and that many differences between the effects of attention on perceptual processing can be explained by differences in the underlying representational structures. Moving forward, it can thus be useful to assess how attention changes the structure of the representational spaces over which it operates, which include the spatial organization, feature maps, and object-based coding in visual cortex. This will ultimately add to our understanding of how attention changes the flow of visual information processing more broadly.

The object-based shift direction anisotropy is modulated by the horizontal visual field meridian

Reallocating object-based attention across the visual field meridians is significantly faster horizontally than vertically (termed the shift direction anisotropy; SDA), implicating the meridians in reorienting object-based attention. Here, we tested the modulatory role of the meridians in the emergence of the SDA by manipulating meridian local feature contrast. Considering the notion of separate pools of attentional resources in each cortical hemisphere, we hypothesised that manipulating the horizontal meridian would selectively modulate the SDA. In four experiments, participants were presented with an "L"-shaped object and detected a target that appeared at either a cued location or at one of two equidistant non-cued locations at the far end of the horizontal or vertical object arm. Meridian local feature contrast was manipulated with perceptually strong enhancements (visible lines and colour contrast borders) and perceptually weak enhancements (illusory borders from line texture patterns and inducers). Weak enhancements of the meridians did not significantly modulate SDA magnitude; however, during perceptually strong enhancements of the horizontal meridian, the SDA was significantly reduced compared with both vertical meridian enhancement and no-enhancement conditions. Moreover, horizontal and vertical shift RTs were statistically equivalent when the horizontal meridian was enhanced with a visible line, our strongest manipulation, indicating the SDA was eliminated. These results suggest that the SDA emerges due to reallocating object-based attention across the horizontal meridian. We interpret this finding as evidence in support of the theory by which anatomical segregations of the visual system determine how pools of attentional resources resolve competition between and within cortical hemispheres.

A Diffusion Model Analysis of Object-Based Selective Attention in the Eriksen Flanker Task

Selective attention might be space-, feature-, and/or object-based. Clear support for the involvement of an object-based mechanism is rather scarce, possibly because the predictions of models from these different classes often overlap. Yet, only object-based models can account for a larger congruency effect (CE) in the Eriksen flanker task when flankers are more (vs. less) strongly grouped to the target, but spacing and other response-irrelevant features of target and flankers are held constant. Exactly this was observed by Kramer and Jacobson (1991). So far, this theoretically relevant finding has not been replicated closely. We replicated the finding in two web-based experiments. Specifically, CEs were larger when flanker lines were connected to the central target line (vs. to outer neutral lines). We also successfully fitted the Diffusion Model for Conflict tasks (DMC) to the experimental data. Critically, diffusion modeling (DMC) and distributional analyses (delta functions) revealed that object membership primarily affected target processing strength rather than strength or timing of flanker processing. This challenges the prominent attentional spreading (sensory enhancement) account of object-based selective attention and motivates an alternative target attenuation account.