Serial Search Task Research Articles

Implicit Spoken Words and Motor Sequences Learning Are Impaired in Children with Specific Language Impairment.

This study aims to compare verbal and motor implicit sequence learning abilities in children with and without specific language impairment (SLI). Forty-eight children (24 control and 24 SLI) were administered the Serial Search Task (SST), which enables the simultaneous assessment of implicit spoken words and visuomotor sequences learning. Results showed that control children implicitly learned both the spoken words as well as the motor sequences. In contrast, children with SLI showed deficits in both types of learning. Moreover, correlational analyses revealed that SST performance was linked with grammatical abilities in control children but with lexical abilities in children with SLI. Overall, this pattern of results supports the procedural deficit hypothesis and suggests that domain general implicit sequence learning is impaired in SLI.

Divergent thinking and differential focusing of perceptual attention in visual serial search tasks

Seminal creativity theories developed by Eysenck and Martindale bring distinguishing predictions to bear on relations between divergent thinking and attention. Drawing upon these theories, the current study was intended to investigate whether the differential focusing of perceptual attention accommodated within visual serial search tasks relates to divergent thinking. An elementary cognitive task was employed to simulate focused perceptual attention and a cognitive inhibition task to simulate defocused perceptual attention. The data obtained lend support to both theories: The attentional distraction scores were more consistent with Martindale's theory, and the attentional selection scores with Eysenck's theory. The theories of Martindale and Eysenck are considered as complementary rather than mutually exclusive, relative to the differential focusing of perceptual attention in visual serial search tasks with respect to divergent thinking.

Top-down but not bottom-up visual scanning is affected in hereditary pure cerebellar ataxia.

The aim of this study was to clarify the nature of visual processing deficits caused by cerebellar disorders. We studied the performance of two types of visual search (top-down visual scanning and bottom-up visual scanning) in 18 patients with pure cerebellar types of spinocerebellar degeneration (SCA6: 11; SCA31: 7). The gaze fixation position was recorded with an eye-tracking device while the subjects performed two visual search tasks in which they looked for a target Landolt figure among distractors. In the serial search task, the target was similar to the distractors and the subject had to search for the target by processing each item with top-down visual scanning. In the pop-out search task, the target and distractor were clearly discernible and the visual salience of the target allowed the subjects to detect it by bottom-up visual scanning. The saliency maps clearly showed that the serial search task required top-down visual attention and the pop-out search task required bottom-up visual attention. In the serial search task, the search time to detect the target was significantly longer in SCA patients than in normal subjects, whereas the search time in the pop-out search task was comparable between the two groups. These findings suggested that SCA patients cannot efficiently scan a target using a top-down attentional process, whereas scanning with a bottom-up attentional process is not affected. In the serial search task, the amplitude of saccades was significantly smaller in SCA patients than in normal subjects. The variability of saccade amplitude (saccadic dysmetria), number of re-fixations, and unstable fixation (nystagmus) were larger in SCA patients than in normal subjects, accounting for a substantial proportion of scattered fixations around the items. Saccadic dysmetria, re-fixation, and nystagmus may play important roles in the impaired top-down visual scanning in SCA, hampering precise visual processing of individual items.

Subjective report of eye fixations during serial search.

Humans readily introspect upon their thoughts and their behavior, but how reliable are these subjective reports? In the present study, we explored the consistencies of and differences between the observer's subjective report and actual behavior within a single trial. On each trial of a serial search task, we recorded eye movements and the participants' beliefs of where their eyes moved. The comparison of reported versus real eye movements revealed that subjects successfully reported a subset of their eye movements. Limits in subjective reports stemmed from both the number and the type of eye movements. Furthermore, subjects sometimes reported eye movements they actually never made. A detailed examination of these reports suggests that they could reflect covert shifts of attention during overt serial search. Our data provide quantitative and qualitative measures of observers' subjective reports and reveal experimental effects of visual search that would otherwise be inaccessible.

Functional size of human visual area V1: A neural correlate of top–down attention

Heavy demands are placed on the brain's attentional capacity when selecting a target item in a cluttered visual scene, or when reading. It is widely accepted that such attentional selection is mediated by top–down signals from higher cortical areas to early visual areas such as the primary visual cortex (V1). Further, it has also been reported that there is considerable variation in the surface area of V1. This variation may impact on either the number or specificity of attentional feedback signals and, thereby, the efficiency of attentional mechanisms. In this study, we investigated whether individual differences between humans performing attention-demanding tasks can be related to the functional area of V1. We found that those with a larger representation in V1 of the central 12° of the visual field as measured using BOLD signals from fMRI were able to perform a serial search task at a faster rate. In line with recent suggestions of the vital role of visuo-spatial attention in reading, the speed of reading showed a strong positive correlation with the speed of visual search, although it showed little correlation with the size of V1. The results support the idea that the functional size of the primary visual cortex is an important determinant of the efficiency of selective spatial attention for simple tasks, and that the attentional processing required for complex tasks like reading are to a large extent determined by other brain areas and inter-areal connections.

Task- and response related dissociations between neglect in near and far space: a morphometric case study.

Introduction: Patients with unilateral neglect may show line bisection errors selectively in either near (within hand reaching) or far (beyond hand reaching) space which suggests that these two spatial areas are coded differently by the brain. This exploratory study investigated, whether any difference in performance between these spatial domains might be task-independent or modulated by the requirement for a motor response.Methods: A 31-year-old right brain damaged patient (MF) and a group of age matched healthy controls were assessed with two serial visual search tasks and a Landmark paradigm. Both types of task required either a directional (pointing) or non-directional (button press) motor response. Participants were assessed with both task types and response modes in near (57 cm) and far space (114 cm).Results: MF showed left neglect during visual search only in far space for the perceptual condition and in near space for the motor condition. MF showed no neglect in both versions of the Landmark task irrespective of spatial distance. A voxel-based morphometric assessment of MF's brain lesion showed marked damage in the right ventro-temporal cortex, superior temporal gyrus, insula, inferior frontal gyrus, angular gyrus and bilaterally in the posterior cingulate cortex.Conclusions: Our preliminary findings suggest that processing of far space during visual search is associated with ventral stream damage but only when space is coded through visual information. Neglect involving directional motor activity in near space seems to be associated with damage of structures sharing close connections with the dorsal stream.

Task- and Response Related Dissociations between Neglect in Near and Far Space: A Morphometric Case Study

Introduction: Patients with unilateral neglect may show line bisection errors selectively in either near (within hand reaching) or far (beyond hand reaching) space which suggests that these two spatial areas are coded differently by the brain. This exploratory study investigated, whether any difference in performance between these spatial domains might be task-independent or modulated by the requirement for a motor response.Methods: A 31-year-old right brain damaged patient (MF) and a group of age matched healthy controls were assessed with two serial visual search tasks and a Landmark paradigm. Both types of task required either a directional (pointing) or non-directional (button press) motor response. Participants were assessed with both task types and response modes in near (57 cm) and far space (114 cm).Results: MF showed left neglect during visual search only in far space for the perceptual condition and in near space for the motor condition. MF showed no neglect in both versions of the Landmark task irrespective of spatial distance. A voxel-based morphometric assessment of MF's brain lesion showed marked damage in the right ventro-temporal cortex, superior temporal gyrus, insula, inferior frontal gyrus, angular gyrus and bilaterally in the posterior cingulate cortex.Conclusions: Our preliminary findings suggest that processing of far space during visual search is associated with ventral stream damage but only when space is coded through visual information. Neglect involving directional motor activity in near space seems to be associated with damage of structures sharing close connections with the dorsal stream.

Dissociation between the procedural learning of letter names and motor sequences in developmental dyslexia

Motor sequence learning has been studied extensively in Developmental dyslexia (DD). The purpose of the present research was to examine procedural learning of letter names and motor sequences in individuals with DD and control groups. Both groups completed the Serial Search Task which enabled the assessment of learning of letter names and motor sequences independently of each other. Control participants learned both the letter names as well as the motor sequence. In contrast, individuals with DD were impaired in learning of the letter names sequence and showed a reliable transfer of the motor sequence. Previous studies proved that motor sequence learning is impaired in DD. The present study demonstrated that this deficit is more pronounced when the task to be learned involves linguistic units. This result implies that the procedural learning system of language is more deficient than the motor procedural learning system in individuals with DD. The dissociation between motor and letter names sequence learning in those with DD also implies that the systems underlying these two tasks are separable.

On the modularity of implicit sequence learning: Independent acquisition of spatial, symbolic, and manual sequences

Learning sequential structures is of fundamental importance for a wide variety of human skills. While it has long been debated whether implicit sequence learning is perceptual or response-based, here we propose an alternative framework that cuts across this dichotomy and assumes that sequence learning rests on associative changes that can occur concurrently in distinct processing systems and support the parallel acquisition of multiple uncorrelated sequences. In three experiments we used a serial search task to test critical predictions of this framework. Experiments 1 and 2 showed that participants learnt uncorrelated sequences of auditory letters and manual responses, as well as sequences of visual letters, spatial locations, and manual responses simultaneously, as indicated by a reliable response time (RT) cost incurred by occasional deviants violating either of the sequences. This RT cost was reliable even when participants showing explicit knowledge were excluded. In Experiment 3 learning of spatial and nonspatial sequences was functionally dissociated: whereas a spatio-motor distractor task disrupted learning of location but not of letter sequences, a phonological distractor task had the reverse effect. The distractor tasks thus did not reduce unspecific attentional resources, but selectively disrupted the formation of sequential associations within spatial and nonspatial processing dimensions. These results support the view that implicit sequence learning rests on experience-dependent changes that can occur in parallel in multiple processing systems involved in spatial attention, object recognition, phonological processing, and manual response selection. The resulting dimension-specific sequence representations support independent predictions of what will appear next, where it will appear, and how one will have to respond to it.

Visual search deficits are independent of magnocellular deficits in dyslexia

The aim of this study was to investigate the theory that visual magnocellular deficits seen in groups with dyslexia are linked to reading via the mechanisms of visual attention. Visual attention was measured with a serial search task and magnocellular function with a coherent motion task. A large group of children with dyslexia (n = 70) had slower serial search times than a control group of typical readers. However, the effect size was small (η(p)(2) = 0.05) indicating considerable overlap between the groups. When the dyslexia sample was split into those with or without a magnocellular deficit, there was no difference in visual search reaction time between either group and controls. The data suggest that magnocellular sensitivity and visual spatial attention weaknesses are independent of one another. They also provide more evidence of heterogeneity in response to psychophysical tasks in groups with dyslexia. Alternative explanations for poor performance on visual attention tasks are proposed along with avenues for future research.

Comparing eye scan path with a single stroke that passes over all items in serial visual search task.

Comparing eye scan path with a single stroke that passes over all items in serial visual search task.

Visual search in children with ADHD: The influence of feedback on selective attention

There is an ongoing debate whether there is a primary deficit in visual selective attention in childhood attention deficit-/hyperactivity disorder (ADHD). We explored this question using a visual search paradigm, in which participants searched for a target that either 'popped out' of the display (a parallel search) or was difficult to find (a serial search). If visual selective attention is impaired in children with ADHD they should perform similarly to normally developing children in parallel search tasks, but should show poorer performance in serial search tasks. As motivation is an important influence on selective attention, particularly in children with ADHD, we also tested the hypothesis that children with ADHD can improve their performance in serial search tasks for a reward. We first developed and validated visual search tasks suitable for children with normally developing control participants. Children had to search for a pig wearing a blue hat and a green tie. We manipulated search type (feature or conjunction search tasks), set size, and feedback (correct/incorrect or reward). The results showed parallel search for feature search tasks and serial search for conjunction search tasks. We then compared children with ADHD with non-clinical controls using these new visual search tasks. Our results showed that children with ADHD and those in the control group were influenced similarly regarding RT and accuracy, by search type and set size, but differently by feedback. That is, children with ADHD and the control children did not differ in the reward feedback condition; however, in the correct/incorrect feedback condition children with ADHD were slower. Overall, these results suggest that children with ADHD show no specific deficits in selective attention but show poorer performance when external motivators are lacking. Therefore, our results support the hypothesis that self-regulation of effort may be the core deficit of children with ADHD.

Right hemisphere dominance in attentional processing and spatiotopic representation of visual stimuli during serial search tasks

Right hemisphere dominance in attentional processing and spatiotopic representation of visual stimuli during serial search tasks

Executive working memory load does not compromise perceptual processing during visual search: Evidence from additive factors analysis

Executive working memory (WM) load reduces the efficiency of visual search, but the mechanisms by which this occurs are not fully known. In the present study, we assessed the effect of executive load on perceptual processing during search. Participants performed a serial oculomotor search task, looking for a circle target among gapped-circle distractors. The participants performed the task under high and low executive WM load, and the visual quality (Experiment 1) or discriminability of targets and distractors (Experiment 2) was manipulated across trials. By the logic of the additive factors method (Sternberg, 1969, 1998), if WM load compromises the quality of perceptual processing during visual search, manipulations of WM load and perceptual processing difficulty should produce nonadditive effects. Contrary to this prediction, the effects of WM load and perceptual difficulty were additive. The results imply that executive WM load does not degrade perceptual analysis during visual search.

Free Classification as a Window on Executive Functioning in Autism Spectrum Disorders

Spontaneous classification was assessed using a free serial search task in 18 school-aged children at the high functioning end of the autistic spectrum and compared with results from age-matched typically developing controls. The task required participants to touch shapes in an exhaustive non-repetitive sequence. The positions of the items varied randomly between touches. The objective was to measure the extent to which children with autism and Asperger's syndrome could spontaneously utilise category information such as shape and color to organise their search. There were no group differences on measures of sequential control and levels of categorization once age and IQ had been partialled out. The results are contrasted with findings from the same lab using a size seriation task.

Spatial working memory maintenance: Does attention play a role? A visual search study

Recent studies have proposed that a common mechanism may underlie spatial attention and spatial working memory. One proposal is that spatial working memory is maintained by attention-based rehearsal [Awh, E., Jonides, J., & Reuter-Lorenz, P. A. (1998). Rehearsal in spatial working memory. Journal of Experimental Psychology: Human Perception and Performance, 24(3), 780–790], and so a spatial attention shift during the retention interval of a spatial location should impair its memory performance. In the present study, participants engaged in single-item, parallel or serial search tasks while remembering a spatial location. Although memory tended to bias all searches, the need for an attentional shift during the retention interval impaired memory performance only in single-item search, but not in other searches. These findings suggest that previous evidence for the attention-based rehearsal account does not generalize to visual search. Results are discussed with regard to the relationship between spatial attention and spatial working memory.

Impaired Serial Visual Search in Children with Developmental Dyslexia

In order to test the hypothesis of attentional deficits in dyslexia, we investigated the performance of children with developmental dyslexia on a number of visual search tasks. When tested with conjunction tasks for orientation and form using complex, letter-like material, dyslexic children showed an increased number of errors accompanied by faster reaction times in comparison to control children matched to the dyslexics on age, gender, and intelligence. On conjunction tasks for orientation and color, dyslexic children were also less accurate, but showed slower reaction times than the age-matched control children. These differences between the two groups decreased with increasing age. In contrast to these differences, the performance of dyslexic children in feature search tasks was similar to that of control children. These results suggest that children with developmental dyslexia present selective deficits in complex serial visual search tasks, implying impairment in goal-directed, sustained visual attention.

The identity intrusion effect: Attentional capture or perceptual load?

Theeuwes and Burger (1998) concluded that irrelevant colour singletons can capture attention within the context of a serial search task by showing that the identity of these singletons can intrude on target processing. However, other researchers have suggested that such distractor interference may arise from a passive, capacity-based selection mechanism that processes all display items automatically and in parallel across the visual field until attentional resources are consumed (Lavie, 1995). According to this perceptual load hypothesis, distractor interference should occur when perceptual load is low but not when perceptual load is high. The present study investigated whether the observed identity intrusion effect was due to attentional capture or perceptual load. Experiment 1 replicated the main findings reported by Theeuwes and Burger under conditions of relatively low perceptual load. Experiment 2 provided critical evidence for the perceptual load account by showing that the identity intrusion effect occurred in the context of low perceptual load, but not high perceptual load. The present findings were therefore interpreted to support the perceptual load account of the identity intrusion effect, not the attentional capture account.

Haptic search with finger movements: using more fingers does not necessarily reduce search times

Two haptic serial search tasks were used to investigate how the separations between items, and the number of fingers used to scan them, influence the search time and search strategy. In both tasks participants had to search for a target (cross) between a fixed number of non-targets (circles). The items were placed in a straight line. The target's position was varied within blocks, and inter-item separation was varied between blocks. In the first experiment participants used their index finger to scan the display. As expected, search time depended on target position as well as on item separation. For larger separations participants' movements were jerky, resembling 'saccades' and 'fixations', while for the shortest separation the movements were smooth. When only considering time in contact with an item, search times were the same for all separation conditions. Furthermore, participants never continued their movement after they encountered the target. These results suggest that participants did not use the time during which they were moving between the items to process information about the items. The search times were a little shorter than those in a static search experiment (Overvliet et al. in Percept Psychophys, 2007a), where multiple items were presented to the fingertips simultaneously. To investigate whether this is because the finger was moving or because only one finger was stimulated, we conducted a second experiment in which we asked participants to put three fingers in line and use them together to scan the items. Doing so increased the time in contact with the items for all separations, so search times were presumably longer in the static search experiment because multiple fingers were involved. This may be caused by the time that it takes to switch from one finger to the other.

Attentional capture in serial audiovisual search tasks

The phenomenon of attentional capture has typically been studied in spatial search tasks. Dalton and Lavie recently demonstrated that auditory attention can also be captured by a singleton item in a rapidly presented tone sequence. In the experiments reported here, we investigated whether these findings extend cross-modally to sequential search tasks using audiovisual stimuli. Participants searched a stream of centrally presented audiovisual stimuli for targets defined on a particular dimension (e.g., duration) in a particular modality. Task performance was compared in the presence versus absence of a unique singleton distractor. Irrelevant auditory singletons captured attention during visual search tasks, leading to interference when they coincided with distractors but to facilitation when they coincided with targets. These results demonstrate attentional capture by auditory singletons during nonspatial visual search.