Biology subjects

Andersen, S. K.

Publications and source records attributed to Andersen, S. K..

5 recordsLinked to original sources

bioRxiv2025

Object speed and distractor number do not affect attentional allocation in multiple object tracking

Keeping track of multiple moving objects across dynamic real-world scenarios such as driving, team sports, or crowded social environments is a fundamental challenge for visual attention. We have previously demonstrated that as the number of tracked objects increases, the strength of attentional facilitation allocated to each individual object decreases, limiting tracking success. It is also well established that beyond the number of tracked objects, faster-moving objects and objects embedded amongst higher numbers of distractors are more difficult to track. Are these effects on tracking difficulty also mediated by less effective allocation of attention to tracked targets as in the case of tracking more targets? If so, one should expect the strength of attentional modulation to drop systematically with increasing speed and total number of moving stimuli. In two experiments (total n = 70), participants were instructed to track moving targets amongst identical distractors while we manipulated object speed (Experiment 1) and number (Experiment 2). As expected, tracking performance declined with both manipulations. However, steady-state visual evoked potentials (SSVEPs) recorded during successful tracking revealed that attentional enhancement of tracked targets compared with distractors did not drop with increasing speed or object number. In summary, bottom-up changes in the stimulus display and top-down attentional manipulations affect tracking performance in independent ways, with the balance between strength of attentional allocation and bottom-up demands of the task determining successful tracking. The allocation of attention itself seems to be determined exclusively by top-down goals rather than being reactive to bottom-up display characteristics. Open Practices StatementParticipant level data and analysis code for all experiments are available at (https://osf.io/ypgfs/) and Experiment 1 was preregistered (https://osf.io/pxh25/). Significance statementKeeping track of multiple moving objects is fundamental to navigating dynamic real-world scenarios. This ability is accomplished through multifocal attentional selection, which weakens as the number of tracked targets increases. This study asks whether other stimulus manipulations increase tracking difficulty by diluting attentional allocation. Using steady-state visual evoked potentials to measure selective attention during tracking, we demonstrate that both increases in speed and distractor number impair performance, however, they do not affect attentional enhancement of targets. This suggests that top-down attentional control operates independently from bottom-up demands.

neuroscience↗

bioRxiv2024

Suppressive interactions between nearby stimuli in visual cortex reflect crowding

Crowding is a phenomenon in which visual object identification is impaired by the close proximity of other stimuli. The neural processes leading to object recognition and its breakdown as seen in crowding are still debated. To assess how crowding affects the processing of stimuli in the visual cortex, we recorded steady-state visual evoked potentials (SSVEPs) elicited by flickering target and flanker stimuli while manipulating the spacing of these stimuli (Experiment 1) as well as target similarity (Experiment 2). Participants performed an orientation discrimination task while accuracy and speed of behavioural responses, along with frequency-tagged SSVEPs elicited by target and flanker stimuli, were recorded. Decreasing target-flanker distance reduced both behavioural performance and target-elicited SSVEP amplitudes. Estimates of the critical spacing, a measure of the spatial extent of crowding, from both behavioural data and SSVEP amplitudes were similar. Additionally, manipulating target similarity affected both measures in the same way. These findings establish a clear connection between the suppression of stimulus processing by nearby flankers in the visual cortex and crowding, and demonstrate the usefulness of SSVEPs in studying the cortical mechanisms of visual crowding.

neuroscience↗

bioRxiv2023

Attention to Colour: Spotlight in Hue Space

Biological systems must allocate limited perceptual resources to relevant elements in their environment. This often requires simultaneous selection of multiple elements from the same feature dimension (e.g., colour). To establish the determinants of divided attentional selection of colour, we conducted an experiment that used multicoloured displays with four overlapping random dot kinematograms that differed only in hue. We manipulated (1) requirement to focus attention to a single colour or divide it between two colours; (2) distances of distractor hues from target hues in a perceptual colour space. We conducted a behavioural and an electroencephalographic experiment, in which each colour was tagged by a specific flicker frequency and driving its own steady-state visual evoked potential. Behavioural and neural indices of attention showed several major consistencies. Concurrent selection halved the neural signature of target enhancement observed for single targets, consistent with an approximately equal division of limited resources between two hue-selective foci. Distractors interfered with behavioural performance in a context-dependent fashion but their effects were asymmetric, indicating that perceptual distance did not adequately capture attentional distance. These asymmetries point towards an important role of higher-level mechanisms such as categorisation and grouping-by-colour in determining the efficiency of attentional allocation in complex, multi-coloured scenes.

neuroscience↗

bioRxiv2022

Attentional enhancement of tracked stimuli in early visual cortex has strict capacity limits

Keeping track of the location of multiple simultaneously moving objects is one of the well documented functions of visual spatial attention. However, the mechanism of attentional selection that supports continuous tracking of several items is unclear. In particular, it has been proposed that target selection in early visual cortex occurs in parallel, with tracking errors arising due to attentional limitations at later processing stages. Here we examine whether, instead, total attentional capacity for enhancement of early visual processing of tracked targets is shared between all attended stimuli. If the magnitude of attentional facilitation of multiple tracked targets was a key limiting factor of tracking ability, then one should expect it to drop systematically with increasing set-size of tracked targets. Human observers (male and female) were instructed to track two, four, or six moving objects among a pool of identical distractors. Steady-state visual evoked potentials (SSVEPs) recorded during the tracking period revealed that the processing of tracked targets was consistently amplified compared to the processing of the distractors. The magnitude of this amplification decreased with increasing set size, and at lateral occipital electrodes it closely followed inverse proportionality to the number of tracked items, suggesting that limited attentional resources must be shared among the tracked stimuli. Accordingly, the magnitude of attentional facilitation predicted the behavioural outcome at the end of the trial. Together, these findings demonstrate that the limitations of multiple object tracking across set-sizes stem from the limitations of top-down selective attention already at the early stages of visual processing. Significance statementThe ability to selectively attend to relevant features or objects is the key to flexibility of perception and action in the continuously changing environment. This ability is demonstrated in the Multiple Object Tracking task where observers monitor multiple independently moving objects at different locations in the visual field. The role of early attentional enhancement in tracking was previously acknowledged in the literature, however, the limitations on tracking were thought to arise during later stages of processing. Here, we demonstrate that the strength of attentional facilitation depends on the number of tracked objects and predicts successful tracking performance. Thus, it is the limitations of attentional enhancement at the early stages of visual processing that determine behavioral performance limits.

animal behavior and cognition↗

bioRxiv2021

Dynamic interplay between reward and voluntary attention determines stimulus processing in visual cortex

Reward enhances stimulus processing in the visual cortex, but the mechanisms through which this effect occurs remain unclear. Reward prospect can both increase the deployment of voluntary attention and increase the salience of previously neutral stimuli. In this study we orthogonally manipulated reward and voluntary attention while human participants performed a global motion detection task. We recorded steady-state visual evoked potentials (SSVEPs) to simultaneously measure the processing of attended and unattended stimuli linked to different reward probabilities, as they compete for attentional resources. The processing of the high rewarded feature was enhanced independently of voluntary attention, but this gain diminished once rewards were no longer available. Neither the voluntary attention nor the salience account alone can fully explain these results. Instead, we propose how these two accounts can be integrated to allow for the flexible balance between reward-driven increase in salience and voluntary attention.

neuroscience↗