Effects Of Spatial Attention Research Articles

Attentional modulation of the somatosensory mu rhythm

Neural oscillations with a frequency of around 10 Hz are thought to be a ubiquitous phenomenon in sensory cortices, and it has been hypothesized that the level of 10 Hz activity is related to local cortical excitability. During spatial attention, the visual alpha rhythm has been found to be modulated according to the direction of attention. Specifically, the alpha rhythm desynchronizes over visual cortex contralateral to the direction of attention and synchronizes over visual cortex ipsilateral to the direction of attention, and these modulations have been associated with facilitation and inhibition of sensory processing. In the somatosensory domain, the reactivity of a similar rhythm, known as the mu rhythm, during attention tasks is a current topic of inquiry and somatotopic modulation of the mu rhythm by directed attention have been reported. In this paper, we investigate how lateralized spatial attention modulates the ongoing somatosensory mu rhythm, and how such modulation impacts sensory information processing. 128 channel EEG was recorded while subjects performed a somatosensory spatial attention task. In addition to analyses on scalp recorded data, a spatial filtering method was utilized to investigate spatial attention effects in the source space. The direction of spatial attention was found to have a significant somatotopic effect on the ongoing mu rhythm occurring in primary somatosensory cortex. Concurrently, the visual alpha rhythm was significantly elevated above the baseline level during somatosensory attention, demonstrating a cross-modal effect. Lastly, an analysis was performed to investigate the correlation between the level of prestimulus mu activity and subsequent stimulus evoked activity in primary somatosensory cortex.

Cortical mechanisms of auditory spatial attention in a target detection task

The benefits of spatial attention on stimulus processing are thought to diminish with increased distance from the attended location, indicating an attention gradient. Evidence for attention gradients is provided by spatial attention effects on event-related potentials (ERPs) under conditions of rapid stimulus presentation from closely spaced locations. This study was motivated by ecological considerations which suggest that auditory attention is particularly useful for panoramic orienting to intermittent sounds. Auditory ERPs were recorded from a wide range of horizontal locations (180°) while subjects pressed a button to occasional targets at one attended location. Results showed that an ERP component associated with automatic orienting, the P3a, had linear amplitude increases to non-targets as a function of distance from the attended location. A component prior to the P3a with a latency of ~200ms, the P200, showed a similar pattern but only when subjects attended to the left hemifield. When attending to lateral targets frontal slow waves contralateral to the attended location followed the P3a and were attenuated at greater distances from the target location for at least 1s. Results suggest that auditory spatial attention under low cognitive loads modulates orienting responses as a function of distance from the attended location. The slow wave findings show that information about the relation between a stimulus and the attended location persists well beyond the time of initial sensory processing and may involve frontal regions important for maintaining online representations of task set.

Effects of spatial and selective attention on basic multisensory integration.

When participants respond to auditory and visual stimuli, responses to audiovisual stimuli are substantially faster than to unimodal stimuli (redundant signals effect, RSE). In such tasks, the RSE is usually higher than probability summation predicts, suggestive of specific integration mechanisms underlying the RSE. We investigated the role of spatial and selective attention on the RSE in audiovisual redundant signals tasks. In Experiment 1, stimuli were presented either centrally (narrow attentional focus) or at 1 of 3 unpredictable locations (wide focus). The RSE was accurately described by a coactivation model assuming linear superposition of modality-specific activation. Effects of spatial attention were explained by a shift of the evidence criterion. In Experiment 2, stimuli were presented at 3 locations; participants had to respond either to all signals regardless of location (simple response task) or to central stimuli only (selective attention task). The RSE was consistent with task-specific coactivation models; accumulation of evidence, however, differed between the 2 tasks.

Effects of Feature-selective and Spatial Attention at Different Stages of Visual Processing

We investigated mechanisms of concurrent attentional selection of location and color using electrophysiological measures in human subjects. Two completely overlapping random dot kinematograms (RDKs) of two different colors were presented on either side of a central fixation cross. On each trial, participants attended one of these four RDKs, defined by its specific combination of color and location, in order to detect coherent motion targets. Sustained attentional selection while monitoring for targets was measured by means of steady-state visual evoked potentials (SSVEPs) elicited by the frequency-tagged RDKs. Attentional selection of transient targets and distractors was assessed by behavioral responses and by recording event-related potentials to these stimuli. Spatial attention and attention to color had independent and largely additive effects on the amplitudes of SSVEPs elicited in early visual areas. In contrast, behavioral false alarms and feature-selective modulation of P3 amplitudes to targets and distractors were limited to the attended location. These results suggest that feature-selective attention produces an early, global facilitation of stimuli having the attended feature throughout the visual field, whereas the discrimination of target events takes place at a later stage of processing that is only applied to stimuli at the attended position.

The effects of visuospatial attention measured across visual cortex using source-imaged, steady-state EEG

How does attention alter neural responses? Decades of electrophysiological measurements in non-human primates as well as human EEG and fMRI studies have shown that spatial attention modulates firing rates across the visual cortex, but the computations that drive this process are still unclear. Further, while it is well known that attention affects perception, we have only a limited understanding of the link between attentionally driven changes in neural firing rates and subject performance. Here we used a novel human neuroimaging method to measure the effect of spatial attention on neural responses in V1, hMT+, hV4, and the intraparietal sulcus (IPS). Attention altered signals in different ways across the visual cortex: areas V1, hMT+, and IPS exhibited primarily response gain changes while hV4 showed contrast gain modulation. Signals in V1, hMT+, and IPS correlated with contrast detection performance suggesting that behavior can be predicted by population-level signals as early as striate cortex.

Dynamics of Within-, Inter-, and Cross-Modal Attentional Modulation

Numerous studies have demonstrated effects of spatial attention within single sensory modalities (within-modal spatial attention) and the effect of directing attention to one sense compared with the other senses (intermodal attention) on cortical neuronal activity. Furthermore, recent studies have been revealing that the effects of spatial attention directed to a certain location in a certain sense spread to the other senses at the same location in space (cross-modal spatial attention). The present study used magnetoencephalography to examine the temporal dynamics of the effects of within-modal and cross-modal spatial and intermodal attention on cortical processes responsive to visual stimuli. Visual or tactile stimuli were randomly presented on the left or right side at a random interstimulus interval and subjects directed attention to the left or right when vision or touch was a task-relevant modality. Sensor-space analysis showed that a response around the occipitotemporal region at around 150 ms after visual stimulation was significantly enhanced by within-modal, cross-modal spatial, and intermodal attention. A later response over the right frontal region at around 200 ms was enhanced by within-modal spatial and intermodal attention, but not by cross-modal spatial attention. These effects were estimated to originate from the occipitotemporal and lateral frontal areas, respectively. Thus the results suggest different spatiotemporal dynamics of neural representations of cross-modal attention and intermodal or within-modal attention.

Exogenous visual attention prolongs perceived duration

Previous studies have shown that spatial attention prolongs the perceived duration of visual stimuli. Chen and O'Neill (Perception & Psychophysics, 63, 1229-1238, 2001) reported, however, the reversed result and thus challenged the generality of this attention effect. We therefore reinvestigated the influence of spatial attention on the perceived duration of visual stimuli in various experimental settings. In five experiments, perceived duration was longer for validly cued stimuli; thus, spatial attention was found to prolong perceived duration. In a further experiment, the specific conditions were such that neither the attention effect nor the reversed pattern, as found by Chen and O'Neill, emerged. Although we cannot provide a conclusive account of why Chen and O'Neill observed the reversed attention effect, the present results reinforce the generality of the spatial attention effect on perceived duration but also make advisable a systematic examination of the factors that might modulate this effect.

Where does attention go when it moves?: Spatial properties and locus of the attentional repulsion effect

Reliable effects of spatial attention on perceptual measures have been well documented, yet little is known about how attention affects perception of space per se. The present study examined the effects of involuntary shifts of spatial attention on perceived location using a paradigm developed by S. Suzuki and P. Cavanagh (1997) that produces an attentional repulsion effect (ARE). The ARE refers to the illusory displacement of two vernier lines away from briefly presented cues. In Experiment 1, we show that the magnitude of the ARE depends on cue-target distance, indicating that the effects of attention on perceived location are not uniform across the visual field. Experiments 2 and 3 tested whether repulsion occurs away from cue center of mass or from cue contour. Perceived repulsion always occurred away from the cues' center of mass, regardless of the arrangement of the cue contours relative to the vernier lines. Moreover, the magnitude of the ARE varied with shifts in the position of the cues' center of mass. These experiments suggest that the onset of the cue produces a shift of attention to its center of mass rather than to the salient luminance contours that define it, and that this mechanism underlies the ARE.

Effect of attention on cortical processing of sound motion: An EEG study

The onset of motion in an otherwise continuous sound elicits a prominent auditory evoked potential, the so-called motion onset response (MOR). The MOR has recently been shown to be modulated by stimulus-dependent factors, such as velocity, while the possible role of task-dependent factors has remained unclear. Here, the effect of spatial attention on the MOR was investigated in 19 listeners. In each trial, the subject initially heard a free-field sound, consisting of a stationary period and a subsequent period of motion. Then, two successive stationary test tones were presented that differed in location and pitch. Subjects either judged whether or not the starting and final positions of the preceded motion matched the positions of the two test tones (‘motion-focused condition’), or whether or not the test tones were identical in pitch, irrespective of the preceded motion stimulus (‘baseline condition’). These two tasks were presented in separate experimental blocks. The performance level in both tasks was similar. However, especially later portions of the MOR were significantly increased in amplitude when auditory motion was task-relevant. Cortical source localization indicated that this extra activation originated in dorsofrontal areas that have been proposed to be part of the dorsal auditory processing stream. These results support the assumption that auditory motion processing is based on a complex interaction of both stimulus-specific and attentional processes.

Cholinergic Enhancement Augments Magnitude and Specificity of Visual Perceptual Learning in Healthy Humans

Learning through experience underlies the ability to adapt to novel tasks and unfamiliar environments. However, learning must be regulated so that relevant aspects of the environment are selectively encoded. Acetylcholine (ACh) has been suggested to regulate learning by enhancing the responses of sensory cortical neurons to behaviorally relevant stimuli. In this study, we increased synaptic levels of ACh in the brains of healthy human subjects with the cholinesterase inhibitor donepezil (trade name: Aricept) and measured the effects of this cholinergic enhancement on visual perceptual learning. Each subject completed two 5 day courses of training on a motion direction discrimination task, once while ingesting 5 mg of donepezil before every training session and once while placebo was administered. We found that cholinergic enhancement augmented perceptual learning for stimuli having the same direction of motion and visual field location used during training. In addition, perceptual learning with donepezil was more selective to the trained direction of motion and visual field location. These results, combined with previous studies demonstrating an increase in neuronal selectivity following cholinergic enhancement, suggest a possible mechanism by which ACh augments neural plasticity by directing activity to populations of neurons that encode behaviorally relevant stimulus features.

The Attentional Attraction Field: Modeling spatial and temporal effects of spatial attention

The Attentional Attraction Field: Modeling spatial and temporal effects of spatial attention

The Effect of Spatial Attention on Pupil Dynamics

The Effect of Spatial Attention on Pupil Dynamics

Selective attention and perceptual suppression independently modulate contrast change detection

Visual awareness bears a complex relationship to selective attention, with some evidence suggesting they can be operationally dissociated (Koch & Tsuchiya 2007). As a first step in the neurophysiological investigation of this dissociation, we developed a novel paradigm that allows for the independent manipulation of visual attention and stimulus awareness in nonhuman primates using a cued perceptual suppression paradigm. We trained two macaque monkeys to detect a slight decrement in stimulus contrast occurring at random time intervals. This change was applied to one of eight isoeccentric sinusoidal grating stimuli with equal probability. In 80% of trials a preceding cue at the fixation spot indicated the correct position of the contrast change. Previous studies in humans demonstrated that such cuing leads to increased selective attention under similar conditions (Posner et al. 1984). In parallel with behavioral cuing, we used binocular rivalry flash suppression (Wolfe 1984) to render the attended stimuli invisible on half the trials. The combined paradigm allows for independent assessment of the effects of spatial attention and perceptual suppression on the detection threshold of the contrast decrement, as well as on neural responses. Our behavioral results suggest that the visibility of the decrement is affected independently by attention and perceptual state. We will present preliminary electrophysiological data from early visual cortex that suggest independent contributions of these two factors to the modulation of neural responses to a visual stimulus.

Exogenous and endogenous spatial attention effects on visuospatial working memory

In this study, we investigate how exogenous and endogenous orienting of spatial attention affect visuospatial working memory (VSWM). Specifically, we focused on two attentional effects and their consequences on storage in VSWM, when exogenous (Experiment 1) or endogenous (Experiment 2) orienting cues were used. The first effect, known as the meridian effect, is given by a decrement in behavioural performance when spatial cues and targets are presented in locations separated by vertical and/or horizontal meridians. The second effect, known as the distance effect, is given by a decrement in the orienting effects as a function of the spatial distance between cues and targets. Our results revealed a dissociation between exogenous and endogenous orienting mechanisms in terms of both meridian and distance effects. We found that meridian crossing affects performance only when endogenous cues were used. Specifically, VSWM performance with endogenous cueing depended more on the number of meridian crossings than on distance between cue and target. By contrast, a U-shaped distance dependency was observed using exogenous cues. Our findings therefore suggest that exogenous and endogenous orienting mechanisms lead to different forms of attentional bias for storage in VSWM.

Properties of spatial attention in conscious and nonconscious visual information processing

A modified flanker task was used to assess the effects of spatial attention during conscious and nonconscious processing. In line with prior findings, we demonstrated that increasing spatial separation between flankers and probes diminished the differences between reaction times to the incongruent and congruent probe-flanker pairs. This trend occurred even when the identity of flankers was suppressed from awareness by a metacontrast mask, indicating (1) that spatial attention can be allocated to information processed at the nonconscious, in addition to the conscious, levels, (2) that effects of spatial attention at these two levels can be equivalent, and (3) that attention deployed at the nonconscious level of processing can be characterized by a spatial gradient that is nearly identical to that found at the conscious level of processing.

The effects of spatial attention and population receptive field size estimation on fMRI topographic mapping signals

The effects of spatial attention and population receptive field size estimation on fMRI topographic mapping signals

Effects of spatial attention on disparity thresholds in detecting dual targets in the central and peripheral visual field

Effects of spatial attention on disparity thresholds in detecting dual targets in the central and peripheral visual field

Electrophysiological correlates of perceptual reversals for three different types of bistable images

Bistable stimuli, i.e. stable visual images that can be perceived in two mutually exclusive ways, offer unique tools for dissociating perceptual from stimulus-driven changes in visual processing. Recently, event-related potentials (ERPs) have been employed to investigate the time-course of these endogenous changes in visual perception. For example, using a variant of the Necker cube, Kornmeier & Bach (2004, 2005) identified a ‘reversal negativity’ ERP component, i.e. a broad increase in negative potential extending from 200–400msec post-stimulus, for trials in which observers reported perceptual reversals. To further investigate the reversal negativity, as well as possible earlier influences on bistability, the current study employed three different types of bistable stimuli: a modified Rubin's face/vase, a modified Schröder's staircase, and a novel stimulus, Lemmo's cheetahs. Using a 128-channel system, 21 observers viewed flashing bistable stimuli, time-locked to the EEG recording, and indicated reversals by a button-press. Results show clear reversal negativities for all three bistable stimuli. In addition, an effect of early visual spatial attention on figure reversals was implicated by an analysis of the early occipital P1 & N1 ERP components. The P1 & N1 were enhanced for trials in which the observer reported perceptual reversals as compared to trials in which no reversals were reported for the face/vase and staircase, but not for the cheetahs. Taken together these results support a model of bistable perception in which changes in early spatial attention (indicated by P1 & N1 enhancement) modulate reversals (indicated by the reversal negativity).

Combined effects of spatial and feature-based attention in human visual cortex

Combined effects of spatial and feature-based attention in human visual cortex

Temporal dissociation of spatial attention and competition effects between face representations

Scalp event-related potential (ERP) studies in humans indicate that the processing of faces differs from other categories between 130 and 170 ms after stimulus onset, peaking at the occipito-temporal N170. We have recently shown that the N170 response to a face stimulus is strongly reduced when another face - or a non-face object of expertise (Rossion, Kung & Tarr, 2004) - is processed concurrently (Jacques & Rossion, 2004), suggesting that neural representations of individual faces compete in the occipito-temporal cortex. However, this amplitude reduction of the N170 may be related to spatial attentional modulations rather than to a competition between face representations. To test this alternative hypothesis, ERP responses to a lateralized face were recorded while subjects were processing a centrally presented stimulus, either a face or a phase-scrambled face stimulus. Subjects performed either a low-level matching task on the central stimulus - thus allocating minimal attention to the lateralized face -, or a task in which they had to detect the occurrence of the lateralized faces. The results are twofold: first, replicating our previous results, the N170 to the lateralized face was largely reduced, starting at about 130 ms, when the central stimulus was a face relative to the control stimulus. Importantly, this competition effect was of similar amplitude in both attentional conditions. Second, when subjects concentrated on the central stimulus, the N170 to the lateral face was strongly reduced, whether the central stimulus was a face or a scrambled face, i.e. the effects of competition and spatial attention were additive on the N170. Moreover and most importantly, this effect of spatial attention started at about 80 ms after stimulus onset, on the visual P1, much earlier than the competition effect. These results indicate that spatial attention and object competition are distinct mechanisms that both strongly shape the processing of faces in extrastriate cortex.