Spatial and temporal attention revealed by microsaccades

When two masked, to-be-attended targets are presented within approximately half a second of each other, performance on the second target (T2) suffers, relative to when the targets are presented further apart in time or when the first target (T1) can be ignored. This pattern of results is known as the attentional blink (AB). Typically, participants differ with respect to the magnitude of their AB and their overall target accuracy. Despite investigations as to what participant characteristics may influence AB performance (e.g., age, brain damage, or mood state), there has been no focused examination of whether individual differences in cognitive performance measures predict the magnitude of the AB or overall rapid serial visual presentation(RSVP) target accuracy. Our university studentparticipants performed single-target and dual-target RSVP tasks, as well as a selection of cognitive tasks that did not use RSVP presentations, with color, letter, digit, and object stimuli. Overall performance on each of the RSVP targets (T1, T2, and single target) was predicted by speeded manual and vocal identification times to isolated stimuli and by performance with other RSVP targets. However, the magnitude of the AB was predicted only by T1 accuracy, not by any other performance measures. The results suggest that individual differences in AB magnitude do not result from differences in effective RSVP target encoding and are not well explained by varied information-processing abilities.

The three projects documented in this thesis investigated the role of three forms of attention in visual processing. Spatial, feature-based and temporal attention. The spatial and feature-based attentional characteristics were studied by conducting extracellular recordings from neurons of area MT and MSTd of macaque visual cortex. While the role of temporal attention was studied in a human psychophysics project. In the physiology projects we first defined the tuning characteristics of neurons from area MT and MSTd for two stimulus dimensions, namely spiral motion stimuli (SMS) and linear motion stimuli (LMS) on the basis of directionality index, the relative frequency of tuned versus untuned neurons, and the individual cells responses to the two forms of stimuli. We found that MT and MSTd showed differential tuning to LMS and SMS. Area MSTd demonstrated better selectivity for SMS as compared to LMS. Conversely, area MT was better tuned to LMS than SMS. Further, we compared spatial and feature-based attentional modulation in area MT and MSTd across SMS and LMS. We found that spatial attention modulates the responses of neurons in both the areas irrespective of the feature dimension defining the attended stimuli. On the other hand feature-based attention was restricted to the stimulus dimension for which an area showed better selectivity, that is SMS for MSTd and LMS for MT. We also observed that the correlation of firing rates with reaction times was restricted to an area’s preferred stimulus dimension. The presence of a significant negative correlation of firing rate with reaction time in area MSTd when attention was directed to its preferred dimension (SMS), indicated that these neurons were involved in perceptual processing of SMS. Similarly, the presence of a significant negative correlation of firing rates with the reaction times in area MT when attention was directed to LMS, provides evidence that MT neurons were involved in perceptual processing of LMS. Taken together, these results show that neurons across the visual cortex are tuned to a range of stimulus dimensions. This multiple stimulus selectivity is thought to be utilized to develop a saliency map (by interaction of bottom-up and top-down processes), which marks the behaviorally relevant aspects of visual space. These behaviorally relevant aspects of the visual space are then preferentially processed throughout the visual hierarchy, and our results suggests that a given area contributes to visual perception by flexibly processing only the stimulus dimension for which it shows best selectivity as a function of stimulus relevance. Finally in human subjects we investigated the temporal characteristics of visual motion processing, using the ‘attentional blink’ paradigm. Attentional blink is a widely studied phenomenon, but almost all studies to the date have been are restricted to stationary stimuli. We here extended this paradigm to motion stimuli. We found the presence of an attentional blink in the motion domain, in that the detection of second of the two target (motion) stimuli was severely degraded when it was presented within 450ms of the first target (motion) stimulus. However, our results were slightly different from the experiments with the stationary stimuli. First, there was an absence of the lag-1 sparing effect typically found with stationary stimuli and second, the time interval over which the attentional blink was observed was about 100ms shorter than typically reported for stationary stimuli. Post-hoc analysis showed that these effects in the motion domain were dependent upon the direction of motion of the first target. Our data showed that when the first target moved in the opposite direction to the second target, there was no attentional blink, but when the first target moved in an orthogonal direction to the second target, there was an attentional blink. These results are in agreement to previous studies showing that the processing of motion stimuli is facilitated when it is preceded by a stimulus moving in opposite directions, while processing of motion stimuli is suppressed when it is preceded by a stimulus moving in an orthogonal direction. Taken together the results of this thesis provides an important contribution to our understanding of the role of attention in visual motion processing. It will be interesting to extend this study in other visual cortical areas and measure spatial and feature-based attention from same set of neurons across different stimulus dimension.

This thesis explores the subjective experience of targets in rapid serial visual presentation (RSVP), an experimental paradigm where visual stimuli are displayed in rapid succession. In RSVP, items appear on the screen so briefly that not every item in the stream can be encoded reliably. Thus, it allows observation of conscious experience at the fringe of perception. The Attentional Blink (AB) - an effect in which an RSVP target is likely to be missed if it follows a fully processed first target - has been used in order to manipulate the accuracy of item identification by varying the target separation and presentation speed. The main focus of studies using RSVP presentation to make inferences about conscious perception has been the question of whether conscious perception is all-or-none or gradual. We initially present some thoughts on the suitability of the AB paradigm for answering this question. Not much is known about the effect of different variables in the paradigm on subjective experience, and it is possible that AB mechanisms affect experience quite differently from other paradigms, limiting the generalisability of findings derived from work within the AB paradigm. Based on this, we follow two lines of evidence: First, we explore the possibility of finding gradations in subjective visibility of targets measured on ratings scales and in the response of the electroencephalogram using a simple single target RSVP. Second, we investigate the effect of target separation and perceived order on this subjective experience in the AB paradigm. Our results indicate that items in single-target RSVP can be perceived in a graded manner, with possible indications of a non-linear jump in brain activity between not-seen and seen items. Regarding subjective experience when separation of two targets is varied, we find a disconnect between accuracy and visibility of the second target when in close proximity to the first, showing relatively low subjective experience considering the high report accuracy. Target separation also affects the number of order confusions, which we find to reduce target visibility under specific conditions. These results add to our understanding of how targets are perceived in RSVP and have implications for research into conscious perception.

Multiple-target visual searches, where more than one target can be present within a single search array, are especially error-prone such that a second target is more likely to be missed after a first target has been detected. This is a serious concern for many critical searches (e.g., radiology, baggage screening) and also raises interesting theoretical questions. Increasingly, evidence supports a resource depletion account of these errors-a first target consumes attentional resources leaving less available to process additional targets. The current study tested this account by comparing 60 participants' multiple-target search performance to two other attention-demanding tasks: attentional blink (AB) and vigilance. The multiple-target search task had 1 or 2 targets per trial intermixed with distractors, and participants clicked on each target they found. The AB task presented two targets (letters) 100-800ms apart in a rapid serial visual presentation (RSVP) stream of distractors (numbers), and participants reported which targets they saw. The vigilance task presented targets (the letter O) in a RSVP stream with distractors (forward or backwards letter Ds) on top of a noise mask, and participants were to indicate every time the target appeared. Second target accuracy in the multiple-target search task significantly correlated with (1) a measure of how long it took second target accuracy in an AB task to recover from the blink, and (2) sensitivity (d') in the vigilance task. Participants who took longer to recover from an AB and who were less vigilant had more second-target misses in a multiple-target search task. Taken together, these results support a resource depletion account of multiple-target search errors in that they highlight an attentional underpinning; errors in AB and vigilance tasks are believed to reflect a deficit in attentional resources and the magnitude of these deficits significantly related to the magnitude of the multiple-target search errors. Meeting abstract presented at VSS 2015. Language: en

What role does attention play in ensuring the temporal precision of visual perception? Behavioural studies have investigated feature selection and binding in time using fleeting sequences of stimuli in the Rapid Serial Visual Presentation (RSVP) paradigm, and found that temporal accuracy is reduced when attentional control is diminished. To reduce the efficacy of attentional deployment, these studies have employed the Attentional Blink (AB) phenomenon. In this article, we use electroencephalography (EEG) to directly investigate the temporal dynamics of conscious perception. Specifically, employing a combination of experimental analysis and neural network modelling, we test the hypothesis that the availability of attention reduces temporal jitter in the latency between a target's visual onset and its consolidation into working memory. We perform time-frequency analysis on data from an AB study to compare the EEG trials underlying the P3 ERPs (Event-related Potential) evoked by targets seen outside vs. inside the AB time window. We find visual differences in phase-sorted ERPimages and statistical differences in the variance of the P3 phase distributions. These results argue for increased variation in the latency of conscious perception during the AB. This experimental analysis is complemented by a theoretical exploration of temporal attention and target processing. Using activation traces from the Neural-ST2 model, we generate virtual ERPs and virtual ERPimages. These are compared to their human counterparts to propose an explanation of how target consolidation in the context of the AB influences the temporal variability of selective attention. The AB provides us with a suitable phenomenon with which to investigate the interplay between attention and perception. The combination of experimental and theoretical elucidation in this article contributes to converging evidence for the notion that the AB reflects a reduction in the temporal acuity of selective attention and the timeliness of perception.

When two targets are presented in a rapid serial visual presentation (RSVP), recognition of the second target (T2) is usually reduced when presented 150-500 ms after the first target, demonstrating an attentional blink (AB). Previous studies have shown a left visual-field (LVF) advantage in T2 recognition, when T2 was embedded in one of two streams, demanding top-down attention for its recognition. Here, we explored the impact of bottom-up saliency on spatial asymmetry in the AB. When T2 was spatially shifted outside from the RSVP, creating an abrupt onset of T2, right T2s showed a right visual-field (RVF) advantage. In lag-1 trials, right T2s were not only better recognized, but also showed a low T1-T2 order error rate. In contrast, recognized left T2s exhibited high order error rate. Without abrupt onset, symmetrical AB was found and order error rate was similarly low in both sides. Follow-up experiments showed that, while RVF advantage was related to bottom-up saliency, order errors were affected by T1 mask. The discrepancy between LVF and RVF advantage in the AB could be resolved in terms of two mechanisms of attentional gating: top-down attentional gating, which is biased towards LVF, and bottom-up attentional gating, which is biased towards RVF.

It has been argued that salient distractor items displayed during rapid serial visual presentation (RSVP) trigger an attentional blink (AB) when they share features with the target item. Here we demonstrate that salient distractor words induce an AB independently of feature overlap with the target. In two experiments a color-highlighted irrelevant word preceded a target by a variable lag in an RSVP series of false font strings. Target identification was reduced at short relative to long temporal lags between the distractor word and the target, irrespective of feature sharing with the distractor word. When the target shared features with the distractor word, target accuracy was reduced across all lags. Accordingly, feature sharing between the distractor word and the target did not amplify the AB, but had an additive effect on attentional capture by the distractor word.

In a randomized, double-blind, and placebo-controlled experiment, the acute effects of gamma-aminobutyric acid (GABA) supplementation on temporal and spatial attention in young healthy adults were investigated. A hybrid two-target rapid serial visual presentation task was used to measure temporal attention and integration. Additionally, a visual search task was used to measure the speed and accuracy of spatial attention. While temporal attention depends primarily on the distribution of limited attentional resources across time, spatial attention represents the engagement and disengagement by relevant and irrelevant stimuli across the visual field. Although spatial attention was unaffected by GABA supplementation altogether, we found evidence supporting improved performance in the temporal attention task. The attentional blink was numerically, albeit not significantly, attenuated at Lag 3, and significantly fewer order errors were committed at Lag 1, compared to the placebo condition. No effect was found on temporal integration rates. Although there is controversy about whether oral GABA can cross the blood-brain barrier, our results offer preliminary evidence that GABA intake might help to distribute limited attentional resources more efficiently, and can specifically improve the identification and ordering of visual events that occur in close temporal succession.

Previous work on visual selective attention in Attention Deficit Hyperactivity Disorder (ADHD) has utilised spatial search paradigms. This study compared ADHD to control children on a temporal search task using Rapid Serial Visual Presentation (RSVP). In addition, the effects of irrelevant singleton distractors on search performance were examined. In each condition, subjects reported the identity of a red letter 'probe' in a sequence of white letters which appeared one after the other at a central fixation point. The temporal position of the probe varied from an initial target, which was distinguished by surrounding asterisks. The target was reported in addition to the probe in condition 2, but not in the baseline condition 1. In a third condition, the initial target was not reported, but one of the asterisks appeared as a colour singleton on some trials. All children displayed an 'attentional blink' with probe detection reduced when it appeared at close temporal relations relative to the target. This 'blink' reduced over time, and there were no group differences in the recovery of performance, although ADHD children made more errors overall. The ADHD group were also more vulnerable than controls to distraction from irrelevant singletons in condition 3. Although the basic mechanisms of selective attention were not impaired in children with ADHD, these children appeared to require more resources to execute the task and were more vulnerable to distraction by irrelevant singletons, indicating deficits in the maintenance of attentional control.

Two experiments examined the possibility that attention directed to a distractor during rapid serial visual presentation (RSVP) can produce an attentional blink (AB). A to-be-ignored distractor (D1) preceded a target word (T2) by a variable lag in RSVP streams of black false-font distractors. D1 was highlighted by color and was a word, a string of consonants, a string of digits, or a string of false-font characters. Recall of T2 was significantly suppressed at short D1-T2 lags (the AB) but only when D1 contained letters; the AB was completely absent when D1 was composed of digits or false-font characters. Thus, the AB can be triggered by a highlighted distractor if the distractor shares features with a target.

Effect of emotions on temporal attention.

Same-object costs and benefits in the object-based attentional blink

Reduced attentional blink for gambling-related stimuli in problem gamblers

Frontal regions of the human cortex are thought to reach full maturation last in the course of development. The present report examines such development in the context of attentional tasks in the temporal (e.g., the attentional blink, AB, paradigm) and spatial (e.g., the visual search, VS, paradigm) domains. Here we show that the recovery from AB is progressively longer with younger age by studying 7-, 12-, 15-year-olds, and adults participating on a modified AB task. By contrast, we found no difference between 7-year-olds and adults in a VS task using the same target stimuli as in the AB task. This differential pattern of development between temporal and spatial attention is discussed in relation to visual working memory development, clinical populations, and general mechanisms of cortical development.

Frontal slowing is not due to a lower preparation rate