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Pseudoneglect in visual search: Behavioral evidence and simulated neural circuitry

eNeuro, 2017-12-19

Video Abstract (AI generated) Paper Preprint eNeuro

Most people tend to bisect horizontal lines slightly to the left of their true center (pseudoneglect), and start visual search from left-sided items. This physiological leftward spatial bias may depend on hemispheric asymmetries in the organization of attentional networks, but the precise mechanisms are unknown. Here we modeled relevant aspects of the ventral and dorsal attentional networks (VAN and DAN) of the human brain. First, we demonstrated pseudoneglect in visual search in 101 right-handed psychology students. Participants consistently tended to start the task from a left-sided item, thus showing pseudoneglect. Second, we trained populations of simulated neurorobots to perform a similar task, by using a genetic algorithm. The neurorobots' behavior was controlled by artificial neural networks, which simulated the human VAN and DAN in the two brain hemispheres. Neurorobots differed in the connectional constraints that were applied to the anatomy and function of the attention networks. Results indicated that (1) neurorobots provided with a biologically plausible hemispheric asymmetry of the VAN-DAN connections, as well as with inter-hemispheric inhibition, displayed the best match with human data; however, (2) anatomical asymmetry per se was not sufficient to generate pseudoneglect; in addition, the VAN must have an excitatory influence on the ipsilateral DAN; (3) neurorobots provided with bilateral competence in the VAN but without inter-hemispheric inhibition failed to display pseudoneglect. These findings provide a proof of concept of the causal link between connectional asymmetries and pseudoneglect, and specify important biological constraints that result in physiological asymmetries of human behavior.

From perception to action: Intracortical recordings reveal cortical gradients of human exogenous attention

Video Abstract (AI generated) Paper Preprint Supplementary Materials&Methods

Exogenous attention, the process that makes external salient stimuli pop-out of a visual scene, is essential for survival. How attention-capturing events modulate processing dynamics in the human brain remains elusive. We obtained a comprehensive depiction of attentional cortical dynamics at high spatiotemporal resolution, by analyzing brain activity from 1,403 intracortical contacts implanted in 28 individuals, while they performed an exogenous attention task. The timing, location and task-relevance of attentional events defined a spatiotemporal continuum of three neural clusters, which mapped onto cortical core-periphery gradients. Attentional effects emerged at the gradient center, where neural activity reflected both visual input and motor output. These results reveal how large-scale neural ensembles, embedded in the cortical hierarchy, underlie the psychological construct of exogenous attention in the human brain.

Fronto-parietal Organization for Response Times in Inhibition of Return: The FORTIOR Model

Cortex, 2017-11-22

Video Abstract (AI generated) Paper Preprint Cortex

Inhibition of Return (IOR) refers to a slowing of response times (RTs) for visual stimuli repeated at the same spatial location, as compared to stimuli occurring at novel locations. The functional mechanisms and the neural bases of this phenomenon remain debated. Here we present FORTIOR, a model of the cortical control of visual IOR in the human brain. The model is based on known facts about the anatomical and functional organization of fronto-parietal attention networks, and accounts for a broad range of behavioral findings in healthy participants and brain-damaged patients. FORTIOR does that by combining four principles of asymmetry: a) Asymmetry in the networks topography, whereby the temporoparietal junction (TPJ) and ventrolateral prefrontal cortex (vlPFC) nodes are lateralized to the right hemisphere, causing higher activation levels in the right intraparietal sulcus (IPS) and frontal eye field (FEF) nodes. b) Asymmetry in inter-hemispheric connectivity, in which inter-hemispheric connections from left hemisphere IPS to right hemisphere IPS and from left hemisphere FEF to right hemisphere FEF are weaker than in the opposite direction. c) Asymmetry of visual inputs, stipulating that the FEF receives direct visual input coming from the ipsilateral visual cortex, while the right TPJ and vlPFC and IPS nodes receive input from both the contralateral and the ipsilateral visual fields. d) Asymmetry in the response modality, with a higher response threshold for the manual response system than that required to trigger a saccadic response. This asymmetry results in saccadic IOR being more robust to interference than manual IOR. FORTIOR accounts for spatial asymmetries in the occurrence of IOR after brain damage and after non-invasive transcranial magnetic stimulation on parietal and frontal regions. It also provides a framework to understand dissociations between manual and saccadic IOR, and makes testable predictions for future experiments to assess its validity.

Evidence Accumulation Modelling Reveals that Gaussian Noise Accounts for Inhibition of Return

Video Abstract (AI generated) Paper Preprint

Inhibition of return (IOR) refers to the slowing of response times (RTs) for stimuli repeated at previously inspected locations, as compared with novel ones. However, the exact processing stage(s) at which IOR occurs, and its nature across different response modalities, remain debated. We tested predictions on these issues originating from the FORTIOR model (fronto-parietal organization of response times in IOR; Seidel Malkinson & Bartolomeo, 2018), and from accumulator models such as LATER (linear approach to threshold with ergodic rate; Carpenter & Williams, 1995). We reanalysed RT data from a target-target IOR paradigm (Bourgeois et al., 2013a, 2013b) by using a Linear Ballistic Accumulator model, to test the predictions of FORTIOR, and specifically whether IOR could occur at early sensory/attentional stages of processing, or at later stages of decision and action selection. We considered the following conditions: manual or saccadic response modality, before or after TMS perturbation over four cortical regions. Results showed that the slope parameter best explained both manual and saccadic IOR, suggesting that in both response modalities IOR may result from slower accumulation of evidence for repeated locations. Additionally, TMS stimulation over the right intra-parietal sulcus (IPS) affected the model's goodness of fit, and the slope parameter best explained the perturbed manual IOR, suggesting that the right IPS might be involved in the accumulation of evidence towards a decision. TMS perturbation over regions that did not affect IOR, nonetheless significantly decreased the goodness of fit of manual IOR models in a nonspecific manner, suggesting that TMS increases intra-individual RT variability. These results support the hypothesis that IOR is a predominantly sensory/attentional phenomenon, and is modulated by activity in fronto-parietal networks.