Biology subjects

Sridharan, D.

Publications and source records attributed to Sridharan, D..

3 recordsLinked to original sources

bioRxiv2018

Exogenous attention facilitates performance through dissociable sensitivity and bias mechanisms

Selective attention enables prioritizing the most important information for differential sensory processing and decision-making. Here, we address an active debate regarding whether attention reflects a unitary phenomenon or involves the operation of dissociable sensory enhancement (perceptual sensitivity) and decisional gating (choice bias) processes. We developed a multialternative task in which participants detected and localized orientation changes in gratings at one of four spatial locations. Exogenous attention cues (high contrast flashes) preceded or followed the change events in close temporal proximity. Analysis of participants behavior with a multidimensional signal detection model revealed markedly distinct effects of exogenous cueing on perceptual sensitivity and choice bias. Whereas sensitivity enhancement was localized to the stimulus proximal to the exogenous cue, bias enhancement occurred even for distal stimuli in the cued hemifield. Modulations of sensitivity and bias were uncorrelated at both cued and uncued locations. Finally, exogenous cueing produced reaction time benefits only at the cued location and costs only at locations contralateral to the cue. These disparate effects of exogenous cueing on sensitivity, bias and reaction times could be parsimoniously explained within the framework of a diffusion-decision model, in which the drift rate was determined by a linear combination of sensitivity and bias at each location. Exogenous cueing effects on sensitivity and bias differed systematically from previously reported effects of endogenous cueing. We propose that the search for shared neural substrates of exogenous and endogenous attention would benefit from investigating neural correlates of their component sensory and decisional mechanisms.\n\nSignificance statementWhen we voluntarily direct attention \"endogenously\", we are able to better perceive stimuli at the attended location (sensitivity), and to prioritize information from that location for guiding behavioral decisions (bias). But when a salient stimulus, such as a flash of lightning, captures our attention \"exogenously\", does it also produce these same effects? To answer this question, we designed a multiple alternative task in which task events occurred in close conjunction with salient exogenous cues (high contrast flashes). We discovered that exogenous attention enhanced both sensitivity and bias for cued stimuli, but each of these changes followed distinct spatial patterns across locations. Our results provide novel insights into component processes of exogenous attention and motivate the search for their neural correlates.

neuroscience↗

bioRxiv2018

The Drosophila Cortactin Binding Protein 2 homolog, Nausicaa, regulates lamellipodial actin dynamics in a Cortactin-dependent manner.

Drosophila CG10915 is an uncharacterized protein coding gene with sequence similarity to human Cortactin Binding Protein 2 (CTTNBP2) and Cortactin Binding Protein 2 N-terminal like (CTTNBP2NL). We have named this gene Nausicaa (naus) and characterize it through a combination of quantitative live-cell total internal reflection fluorescence (TIRF) microscopy, electron microscopy, RNAi depletion, and genetics. We found that Naus co-localizes with F-actin and Cortactin in the lamellipodia of Drosophila S2R+ and D25c2 cells and this localization is lost following Cortactin or Arp2/3 depletion or by mutations that disrupt a conserved proline patch found in its mammalian homologs. Using Permeabilization Activated Reduction in Fluorescence (PARF) and Fluorescence Recovery after Photo-bleaching (FRAP), we find that depletion of Cortactin alters Naus dynamics leading to a decrease in its half-life. Furthermore, we discovered that Naus depletion in S2R+ cells led to a decrease in actin retrograde flow and a lamellipodia characterized by long, unbranched filaments. We demonstrate that these alterations to the dynamics and underlying actin architecture also affect D25c2 cell migration and decrease arborization in Drosophila neurons. We present the novel hypothesis that Naus functions to slow Cortactins disassociation from Arp2/3 nucleated branch junctions, thereby increasing both branch nucleation and junction stability.

cell biology↗

bioRxiv2017

Sensory and decisional components of endogenous attention are dissociable.

Endogenously cueing a stimulus for attention enhances sensory processing of the attended stimulus, and efficiently selects information from the attended stimulus for guiding behavioral decisions. Yet, it is unknown if these sensory and decisional components of endogenous attention are under the control of common, overlapping or distinct mechanisms. Here, we tested human observers in a multi-alternative visuospatial attention task with probabilistic spatial cues, whose predictive validity varied across spatial locations. Observers behavioral choices were analyzed with a multidimensional signal detection model, derived from Bayesian decision theory. The model effectively decoupled attentions effects on perceptual sensitivity from those on decisional thresholds (bias), and revealed striking dissociations between them. Sensitivity was highest at the cued location, and not significantly different among uncued locations, suggesting a spotlight-like allocation of sensory resources at the cued location. On the other hand, bias varied systematically with endogenous cue validity, suggesting a graded distribution of decision thresholds across all locations. Cueing-induced modulations of sensitivity and bias were uncorrelated within and across subjects. Finally, bias selectively correlated with key measures of decision-making: reaction times were strongly correlated with bias, cueing-induced benefits in reaction times were correlated with bias changes independently of sensitivity changes, and subjects who exhibited higher bias, rather than higher sensitivity, toward the cued location produced more optimal behavioral decisions. Our model and findings demonstrate that endogenous cueing of attention does not engage a unitary selection mechanism, but rather involves the operation of dissociable sensory enhancement and decisional selection processes.\n\nSignificance statementThe capacity for selective attention allows us to engage efficiently with the most important objects in the world around us. Attention affects the way we perceive important stimuli and also affects how we make behavioral decisions about these stimuli. In this study, we test human observers on a multiple alternative attention task and show that attentions effects on perceptual processing and decision-making can be dissociated. Specifically, attentions sensory effects alone are in line with the conventional notion of an attentional \"spotlight\". These insights are obtained with a novel Bayesian decision model, which we propose as a powerful tool for teasing apart component processes of cognitive phenomena, and could aid the search for the neural correlates of these phenomena.

neuroscience↗