Publications by authors named "David Pascucci"

19 Publications

  • Page 1 of 1

The anisotropic field of ensemble coding.

Sci Rep 2021 Apr 15;11(1):8212. Epub 2021 Apr 15.

Department of Psychology, University of Fribourg, Fribourg, Switzerland.

Human observers can accurately estimate statistical summaries from an ensemble of multiple stimuli, including the average size, hue, and direction of motion. The efficiency and speed with which statistical summaries are extracted suggest an automatic mechanism of ensemble coding that operates beyond the capacity limits of attention and memory. However, the extent to which ensemble coding reflects a truly parallel and holistic mode of processing or a non-uniform and biased integration of multiple items is still under debate. In the present work, we used a technique, based on a Spatial Weighted Average Model (SWM), to recover the spatial profile of weights with which individual stimuli contribute to the estimated average during mean size adjustment tasks. In a series of experiments, we derived two-dimensional SWM maps for ensembles presented at different retinal locations, with different degrees of dispersion and under different attentional demands. Our findings revealed strong spatial anisotropies and leftward biases in ensemble coding that were organized in retinotopic reference frames and persisted under attentional manipulations. These results demonstrate an anisotropic spatial contribution to ensemble coding that could be mediated by the differential activation of the two hemispheres during spatial processing and scene encoding.
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http://dx.doi.org/10.1038/s41598-021-87620-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8050251PMC
April 2021

Serial dependence does not originate from low-level visual processing.

Cognition 2021 Apr 7;212:104709. Epub 2021 Apr 7.

Laboratory of Psychophysics, Brain Mind Institute, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.

Perception depends not only on the current sensory input but also on the preceding history of stimuli. In serial dependence (SD), for example, the orientation of a Gabor patch is mistakenly reported as more similar to previous trials than it actually is. This bias is typically observed for moderate orientation differences (<45°) and extends over a few trials in the past. It is hotly debated whether SD originates at perceptual or post-perceptual, e.g., decisional, stages. Here, we provide evidence for the latter hypothesis. We presented Gabor patches with different spatial frequencies or Gabors intermingled with dot patterns. Even though stimuli were perceptually clearly dissimilar, we found robust SD effects arguing against any perceptual account. These findings suggest a re-evaluation of current models and theoretical accounts of SD.
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http://dx.doi.org/10.1016/j.cognition.2021.104709DOI Listing
April 2021

Nested oscillations and brain connectivity during sequential stages of feature-based attention.

Neuroimage 2020 12 9;223:117354. Epub 2020 Sep 9.

Perceptual Networks Group, Department of Psychology, University of Fribourg, Fribourg, Switzerland.

Brain mechanisms of visual selective attention involve both local and network-level activity changes at specific oscillatory rhythms, but their interplay remains poorly explored. Here, we investigate anticipatory and reactive effects of feature-based attention using separate fMRI and EEG recordings, while participants attended to one of two spatially overlapping visual features (motion and orientation). We focused on EEG source analysis of local neuronal rhythms and nested oscillations and on graph analysis of connectivity changes in a network of fMRI-defined regions of interest, and characterized a cascade of attentional effects at multiple spatial scales. We discuss how the results may reconcile several theories of selective attention, by showing how β rhythms support anticipatory information routing through increased network efficiency, while reactive α-band desynchronization patterns and increased α-γ coupling in task-specific sensory areas mediate stimulus-evoked processing of task-relevant signals.
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http://dx.doi.org/10.1016/j.neuroimage.2020.117354DOI Listing
December 2020

Connectome spectral analysis to track EEG task dynamics on a subsecond scale.

Neuroimage 2020 11 9;221:117137. Epub 2020 Jul 9.

Connectomics Lab, Dept. of Radiology, University Hospital of Lausanne and University of Lausanne (CHUV-UNIL), Lausanne, Switzerland.

We present an approach for tracking fast spatiotemporal cortical dynamics in which we combine white matter connectivity data with source-projected electroencephalographic (EEG) data. We employ the mathematical framework of graph signal processing in order to derive the Fourier modes of the brain structural connectivity graph, or "network harmonics". These network harmonics are naturally ordered by smoothness. Smoothness in this context can be understood as the amount of variation along the cortex, leading to a multi-scale representation of brain connectivity. We demonstrate that network harmonics provide a sparse representation of the EEG signal, where, at certain times, the smoothest 15 network harmonics capture 90% of the signal power. This suggests that network harmonics are functionally meaningful, which we demonstrate by using them as a basis for the functional EEG data recorded from a face detection task. There, only 13 network harmonics are sufficient to track the large-scale cortical activity during the processing of the stimuli with a 50 ​ms resolution, reproducing well-known activity in the fusiform face area as well as revealing co-activation patterns in somatosensory/motor and frontal cortices that an unconstrained ROI-by-ROI analysis fails to capture. The proposed approach is simple and fast, provides a means of integration of multimodal datasets, and is tied to a theoretical framework in mathematics and physics. Thus, network harmonics point towards promising research directions both theoretically - for example in exploring the relationship between structure and function in the brain - and practically - for example for network tracking in different tasks and groups of individuals, such as patients.
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http://dx.doi.org/10.1016/j.neuroimage.2020.117137DOI Listing
November 2020

A regularized and smoothed General Linear Kalman Filter for more accurate estimation of time-varying directed connectivity

Annu Int Conf IEEE Eng Med Biol Soc 2019 Jul;2019:611-615

Adaptive algorithms based on the Kalman filter are valuable tools to model the dynamic and directed Granger causal interactions between neurophysiological signals simultaneously recorded from multiple cortical regions. Among these algorithms, the General Linear Kalman Filter (GLKF) has proven to be the most accurate and reliable. Here we propose a regularized and smoothed GLKF (spsm-GLKF) with ℓ1 norm penalties based on lasso or group lasso and a fixedinterval smoother. We show that the group lasso penalty promotes sparse solutions by shrinking spurious connections to zero, while the smoothing increases the robustness of the estimates. Overall, our results demonstrate that spsm-GLKF outperforms the original GLKF, and represents a more accurate tool for the characterization of dynamical and sparse functional brain networks.
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http://dx.doi.org/10.1109/EMBC.2019.8857915DOI Listing
July 2019

Getting rid of visual distractors: the why, when, how, and where.

Curr Opin Psychol 2019 10 14;29:135-147. Epub 2019 Feb 14.

Center for Mind/Brain Sciences, University of Trento, Trento, Italy.

Distractor suppression, or the ability to disregard salient distractors while dealing with task-relevant information, is a key component of selective attention. Recent research has shown that distractor suppression can take place in different circumstances and present itself in different guises, which is presumably paralleled by a multiplicity of underlying neural mechanisms. In this review article, we discuss a number of central themes concerning distractor suppression and the underlying neural mechanisms, and also highlight several unresolved issues that will have to be addressed in future investigations.
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http://dx.doi.org/10.1016/j.copsyc.2019.02.004DOI Listing
October 2019

Laws of concatenated perception: Vision goes for novelty, decisions for perseverance.

PLoS Biol 2019 03 5;17(3):e3000144. Epub 2019 Mar 5.

Department of Neuroscience, Biomedicine and Movement Sciences, University of Verona, Verona, Italy.

Every instant of perception depends on a cascade of brain processes calibrated to the history of sensory and decisional events. In the present work, we show that human visual perception is constantly shaped by two contrasting forces exerted by sensory adaptation and past decisions. In a series of experiments, we used multilevel modeling and cross-validation approaches to investigate the impact of previous stimuli and decisions on behavioral reports during adjustment and forced-choice tasks. Our results revealed that each perceptual report is permeated by opposite biases from a hierarchy of serially dependent processes: Low-level adaptation repels perception away from previous stimuli, whereas decisional traces attract perceptual reports toward the recent past. In this hierarchy of serial dependence, "continuity fields" arise from the inertia of decisional templates and not from low-level sensory processes. This finding is consistent with a Two-process model of serial dependence in which the persistence of readout weights in a decision unit compensates for sensory adaptation, leading to attractive biases in sequential perception. We propose a unified account of serial dependence in which functionally distinct mechanisms, operating at different stages, promote the differentiation and integration of visual information over time.
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http://dx.doi.org/10.1371/journal.pbio.3000144DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6400421PMC
March 2019

Desensitizing the attention system to distraction while idling: A new latent learning phenomenon in the visual attention domain.

J Exp Psychol Gen 2018 Dec 25;147(12):1827-1850. Epub 2018 Oct 25.

Department of Neuroscience, Biomedicine, & Movement Sciences, University of Verona.

For the good and the bad, the world around us is full of distraction. In particular, onset stimuli that appear abruptly in the scene grab attention, thus disrupting the ongoing task. Different cognitive mechanisms for distractor filtering have been proposed, but prevalent accounts share the idea that filtering is accomplished to shield target processing from interference. Here we provide novel evidence that challenges this view, as passive exposure to a repeating visual onset is sufficient to trigger learning-dependent mechanisms to filter the unwanted stimulation. In other words, our study shows that during passive exposure the cognitive system is capable of learning about the characteristics of the salient yet irrelevant stimulation, and to reduce the responsiveness of the attention system to it, thus significantly decreasing the impact of the distractor upon start of an active task. However, despite passive viewing efficiently attenuates the spatial capture of attention, a short-lived performance cost is found when the distractor is initially encountered within the context of the active task. This cost, which dissipates in a few trials, likely reflects the need to familiarize with the distractor, already seen during passive viewing, in the new context of the active task. Although top-down inhibitory signals can be applied to distractors for the successful completion of goal-directed behavior, our results emphasize the role of more automatic habituation mechanisms for distraction exclusion based on a neural model of the history of the irrelevant stimulation. (PsycINFO Database Record (c) 2018 APA, all rights reserved).
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http://dx.doi.org/10.1037/xge0000503DOI Listing
December 2018

Gating by induced Α-Γ asynchrony in selective attention.

Hum Brain Mapp 2018 10 24;39(10):3854-3870. Epub 2018 May 24.

Perceptual Networks Group, Department of Psychology, University of Fribourg, Fribourg, Switzerland.

Visual selective attention operates through top-down mechanisms of signal enhancement and suppression, mediated by α-band oscillations. The effects of such top-down signals on local processing in primary visual cortex (V1) remain poorly understood. In this work, we characterize the interplay between large-scale interactions and local activity changes in V1 that orchestrates selective attention, using Granger-causality and phase-amplitude coupling (PAC) analysis of EEG source signals. The task required participants to either attend to or ignore oriented gratings. Results from time-varying, directed connectivity analysis revealed frequency-specific effects of attentional selection: bottom-up γ-band influences from visual areas increased rapidly in response to attended stimuli while distributed top-down α-band influences originated from parietal cortex in response to ignored stimuli. Importantly, the results revealed a critical interplay between top-down parietal signals and α-γ PAC in visual areas. Parietal α-band influences disrupted the α-γ coupling in visual cortex, which in turn reduced the amount of γ-band outflow from visual areas. Our results are a first demonstration of how directed interactions affect cross-frequency coupling in downstream areas depending on task demands. These findings suggest that parietal cortex realizes selective attention by disrupting cross-frequency coupling at target regions, which prevents them from propagating task-irrelevant information.
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http://dx.doi.org/10.1002/hbm.24216DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6866587PMC
October 2018

The relationship between semantic access and introspective awareness.

Brain Cogn 2018 06 5;123:47-56. Epub 2018 Mar 5.

State Key Laboratory of Cognitive Neuroscience and Learning & IDG/McGovern Institute for Brain Research, Beijing Normal University, China; Center for Collaboration and Innovation in Brain and Learning Sciences, Beijing Normal University, China. Electronic address:

There have long been speculations about the relationship between consciousness and language. This study aimed to determine whether an individual's level of introspective awareness, based on self-report, relates to accessibility of their semantic system as evaluated by the N400. Thirty-five university students completed the study. All were right-handed, with normal or corrected-to-normal vision, without known neurological or psychological health issues. They first performed on a lexical decision task while their brain electrophysiological responses were recorded. Then, they provided assessment ratings about their levels of introspective awareness. Analysis revealed moderate to strong correlations (Pearson's rs = 0.49-0.62) between awareness self-ratings and ease of semantic access as indexed by the N400. Correlation between the self-report measure and the objective neurophysiological measure suggests that subjective assessment of awareness may deserve more credibility, which in addition to reflecting subjective perception and evaluation about one's own higher order mental functioning, may also interact with the neurophysiological processes contributive and subject to such awareness. Implications for future research on the role of semantic network in the mechanism of introspective awareness are discussed.
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http://dx.doi.org/10.1016/j.bandc.2018.02.005DOI Listing
June 2018

Independent circuits in basal ganglia and cortex for the processing of reward and precision feedback.

Neuroimage 2017 11 1;162:56-64. Epub 2017 Sep 1.

Center for Mind/Brain Sciences (CIMeC), University of Trento, Rovereto, Italy.

In order to understand human decision making it is necessary to understand how the brain uses feedback to guide goal-directed behavior. The ventral striatum (VS) appears to be a key structure in this function, responding strongly to explicit reward feedback. However, recent results have also shown striatal activity following correct task performance even in the absence of feedback. This raises the possibility that, in addition to processing external feedback, the dopamine-centered "reward circuit" might regulate endogenous reinforcement signals, like those triggered by satisfaction in accurate task performance. Here we use functional magnetic resonance imaging (fMRI) to test this idea. Participants completed a simple task that garnered both reward feedback and feedback about the precision of performance. Importantly, the design was such that we could manipulate information about the precision of performance within different levels of reward magnitude. Using parametric modulation and functional connectivity analysis we identified brain regions sensitive to each of these signals. Our results show a double dissociation: frontal and posterior cingulate regions responded to explicit reward but were insensitive to task precision, whereas the dorsal striatum - and putamen in particular - was insensitive to reward but responded strongly to precision feedback in reward-present trials. Both types of feedback activated the VS, and sensitivity in this structure to precision feedback was predicted by personality traits related to approach behavior and reward responsiveness. Our findings shed new light on the role of specific brain regions in integrating different sources of feedback to guide goal-directed behavior.
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http://dx.doi.org/10.1016/j.neuroimage.2017.08.067DOI Listing
November 2017

Filtering visual onsets via habituation: A context-specific long-term memory of irrelevant stimuli.

Psychon Bull Rev 2018 06;25(3):1028-1034

Department of Psychology, University of Fribourg, Fribourg, Switzerland.

The fact that we are often immediately attracted by sudden visual onsets provides a clear advantage for our survival. However, how can we resist from being continuously distracted by irrelevant repetitive onsets? Since the seminal work of Sokolov (1963), habituation of the orienting of attention has long been proposed to be a possible filtering mechanism. Here, in two experiments, we provide novel evidence showing that (a) habituation of capture of focused visual attention relies on a stored representation of the distractor onsets in relation to their context, and (b) that once formed such representation endures unchanged for weeks without any further exposure to the distractors. In agreement with the proposal of Wagner (1979) concerning the associative nature of habituation, the results of Experiment 1 suggest that habituation of attentional capture is context specific. Furthermore, the results of Experiment 2 show that to filter visual distractors our cognitive system uses long-lasting memories of the irrelevant information. Although distractor filtering can be implemented via top-down inhibitory control, neural and cognitive mechanisms underlying habituation provide a straightforward explanation for the reduced distraction obtained with training, thus working like an automatic filter that prevents irrelevant recurring stimuli from gaining access to higher stages of analysis.
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http://dx.doi.org/10.3758/s13423-017-1320-xDOI Listing
June 2018

Short-term and long-term plasticity in the visual-attention system: Evidence from habituation of attentional capture.

Neurobiol Learn Mem 2016 Apr 27;130:159-69. Epub 2016 Feb 27.

Department of Neurological Sciences, Section of Physiology and Psychology, University of Verona, Italy.

Attention is known to be crucial for learning and to regulate activity-dependent brain plasticity. Here we report the opposite scenario, with plasticity affecting the onset-driven automatic deployment of spatial attention. Specifically, we showed that attentional capture is subject to habituation, a fundamental form of plasticity consisting in a response decrement to repeated stimulations. Participants performed a visual discrimination task with focused attention, while being occasionally exposed to a distractor consisting of a high-luminance peripheral onset. With practice, short-term and long-term habituation of attentional capture emerged, making the visual-attention system fully immune to distraction. Furthermore, spontaneous recovery of attentional capture was found when the distractor was temporarily removed. Capture, however, once habituated was surprisingly resistant to spontaneous recovery, taking from several minutes to days to recover. The results suggest that the mechanisms subserving exogenous attentional orienting are subject to profound and enduring plastic changes based on previous experience, and that habituation can impact high-order cognitive functions.
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http://dx.doi.org/10.1016/j.nlm.2016.02.010DOI Listing
April 2016

Monetary reward modulates task-irrelevant perceptual learning for invisible stimuli.

PLoS One 2015 5;10(5):e0124009. Epub 2015 May 5.

Center for Mind/Brain Sciences, University of Trento, Trento, Italy.

Task Irrelevant Perceptual Learning (TIPL) shows that the brain's discriminative capacity can improve also for invisible and unattended visual stimuli. It has been hypothesized that this form of "unconscious" neural plasticity is mediated by an endogenous reward mechanism triggered by the correct task performance. Although this result has challenged the mandatory role of attention in perceptual learning, no direct evidence exists of the hypothesized link between target recognition, reward and TIPL. Here, we manipulated the reward value associated with a target to demonstrate the involvement of reinforcement mechanisms in sensory plasticity for invisible inputs. Participants were trained in a central task associated with either high or low monetary incentives, provided only at the end of the experiment, while subliminal stimuli were presented peripherally. Our results showed that high incentive-value targets induced a greater degree of perceptual improvement for the subliminal stimuli, supporting the role of reinforcement mechanisms in TIPL.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0124009PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4420259PMC
February 2016

The distracting impact of repeated visible and invisible onsets on focused attention.

J Exp Psychol Hum Percept Perform 2015 Jun 13;41(3):879-92. Epub 2015 Apr 13.

Center of Mind/Brain Sciences, University of Trento.

A sudden peripheral onset is a powerful attentional attractor. However, in real life potentially distracting events do not always occur as a single event, but rather they can occur in a repetitive fashion. Hence, one of the aims of the present study was to investigate how the attentional system reacts to multiple consecutive onsets within the same trial. The results, quite surprisingly, showed that repeated peripheral onsets do not have a negative impact on visual performance, while they confirmed that a single peripheral onset captures focused attention. We hypothesize the existence of a short-term habituation mechanism that prevents visual attention from being continuously distracted by the same task-irrelevant event when this is rapidly repeated. A further aim of the study was to test the proposal according to which subliminal visual transients can bypass the conscious inhibitory control, thus resulting more distracting than supraliminal transients. We did not find in any of the 8 experiments that we conducted that subliminal onsets, either single or repeated, can grab attention when fully focused at fixation. Hence, in the case of sudden onsets, the general claim that task-irrelevant invisible stimuli can be more disturbing than visible ones does not seem to be fully justified.
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http://dx.doi.org/10.1037/xhp0000025DOI Listing
June 2015

Location transfer of perceptual learning: passive stimulation and double training.

Vision Res 2015 Mar 7;108:93-102. Epub 2015 Feb 7.

Center for Mind/Brain Sciences, University of Trento, Corso Bettini 31, 38068 Rovereto, Italy; Department of Psychology and Cognitive Sciences, University of Trento, Corso Bettini 31, 38068 Rovereto, Italy.

Specificity has always been considered one of the hallmarks of perceptual learning, suggesting that performance improvement would reflect changes at early stages of visual analyses (e.g., V1). More recently, however, this view has been challenged by studies documenting complete transfer of learning among different spatial locations or stimulus orientations when a double-training procedure is adopted. Here, we further investigate the conditions under which transfer of visual perceptual learning takes place, confirming that the passive stimulation at the transfer location seems to be insufficient to overcome learning specificity. By contrast, learning transfer is complete when performing a secondary task at the transfer location. Interestingly, (i) transfer emerges when the primary and secondary tasks are intermingled on a trial-by-trial basis, and (ii) the effects of learning generalization appear to be reciprocal, namely the primary task also serves to enable transfer of the secondary task. However, if the secondary task is not performed for a sufficient number of trials, then transfer is not enabled. Overall, the results lend support to the recent view that task-relevant perceptual learning may involve high-level stages of visual analyses.
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http://dx.doi.org/10.1016/j.visres.2015.01.024DOI Listing
March 2015

Immediate effect of internal reward on visual adaptation.

Psychol Sci 2013 Jul 13;24(7):1317-22. Epub 2013 May 13.

Center for Mind/Brain Sciences, Sciences, University ofTrento, Corso Bettini, 31, 38068 Rovereto, Italy.

In the past decade, there has been an increasing interest in the effects of rewards on visual perception. Exogenous rewards have been shown to increase visual sensitivity and to affect attentional selection. Human beings, however, also feel rewarded by the correct execution of a task. It has been proposed that this form of endogenous reward triggers reinforcement signals in the brain, making the sensory system more sensitive to stimuli that have been extensively and repeatedly paired with the rewarding experiences and modulating long-term cortical plasticity. Here, we report the striking observation that a well-known visual illusion, the tilt aftereffect, which is due to a form of short-term cortical plasticity, is immediately enhanced by a concurrent and independent target-recognition process. Our results show that endogenous rewards can alter visual experience with virtually no delay.
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http://dx.doi.org/10.1177/0956797612469211DOI Listing
July 2013

Permeability of priming of pop out to expectations.

J Vis 2012 Sep 29;12(10). Epub 2012 Sep 29.

Center for Mind-Brain Sciences, University of Trento, Rovereto, Italy.

It is well established that repetition of the same target color across consecutive trials enhances search efficiency for pop-out targets; this phenomenon is known as Priming of Pop out (PoP). In three experiments, we addressed whether PoP interacts with top-down expectations in altering target visibility, which was manipulated via metacontrast masking. The target color either remained the same for n consecutive trials (blocked condition) or changed unpredictably (random condition). The results showed that PoP reduced the efficacy of masking and that its beneficial effect can be either potentiated or attenuated by participants' expectations about the upcoming target color. These findings undermine the view that PoP should be impermeable to top-down factors. In addition, we found evidence that both explicit and implicit expectations interact with PoP. The former can be induced via instructions on the rate of alternation of the target color, and the latter can be induced by random sequences in which repetitions of the same target color exceed those predicted by an internal model of randomness for binary events. In the latter case, more than three repetitions of the same target color led to a decline in target visibility. We speculate that, in the random condition, after few repetitions of the same target, participants developed an expectation for a change; this phenomenon is similar to the "gambler's fallacy." Finally, our analyses revealed no effect of expectation on switch trials (i.e., when the target color changed), which casts doubt on the efficacy of top-down control in feature search.
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http://dx.doi.org/10.1167/12.10.21DOI Listing
September 2012

Acoustic cues to visual detection: a classification image study.

J Vis 2011 May 11;11(6). Epub 2011 May 11.

Department of Psychology, University of Florence, Florence, Italy.

A non-informative sound is known to improve contrast detection thresholds for a synchronous visual target (M. Lippert, N. K. Logothetis, & C. Kayser, 2007). We investigated the spatio-temporal characteristics of the mechanisms underlying this crossmodal effect by using a classification image paradigm specifically suited to investigate perceptual templates across both space and time (P. Neri & D. J. Heeger, 2002). A bright bar was embedded in 2D (space-time) dynamic noise and observers were asked to detect its presence in both unimodal (only visual) and bimodal (audio-visual) conditions. Classification image analysis was performed and the 1st and 2nd order kernels were derived. Our results show that the cross-modal facilitation of detection consists in a reduction of activity of the early mechanisms elicited by the onset of the stimulation and not directly involved in the identification of the target. In fact, the sound sharpens the 2nd order kernels (involved in target detection) by suppressing the activation preceding the target, whereas it does not influence the 1st order kernels. These data suggest that the sound affects some non-linear process involved with the detection of a visual stimulus by, decreasing the activity of contrast energy filters temporally uncorrelated with the target, hence reducing temporal uncertainty.
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http://dx.doi.org/10.1167/11.6.7DOI Listing
May 2011