Target Letter Research Articles

Correction: Social Groups Prioritize Selective Attention to Faces: How Social Identity Shapes Distractor Interference.

[This corrects the article DOI: 10.1371/journal.pone.0161426.].

An attention account of neural priming

ABSTRACTRepetition priming of familiar stimuli (e.g., objects) produces a decrease in visual cortical activity for repeated versus novel items, which has been attributed to more fluent processing for repeated items. By contrast, priming of unfamiliar stimuli (e.g., abstract shapes) produces an increase in visual cortical activity. The mechanism for priming-related increases in activity for repeated unfamiliar stimuli is unknown. We hypothesised that such increases in activity may reflect attentional allocation to these items. We tested this hypothesis using a priming-spatial attention paradigm. During Phase 1 of Experiment 1, participants viewed unfamiliar abstract shapes and familiar objects. During Phase 2, participants identified target letters (S or H). Each target letter was preceded by a non-informative shape or object cue that was repeated (from Phase 1) or novel in the same (valid) or opposite (invalid) hemifield. In Experiment 2, we manipulated shape familiarity by presenting shapes once or six times during Phase 1. For both experiments, at valid locations, target identification accuracy was higher following repeated versus novel unfamiliar item cues and lower following repeated versus novel familiar item cues. These findings support our hypothesis that priming-related increases in visual cortical activity for repeated unfamiliar items may, in part, reflect attentional allocation.

Effects of expectation congruency on event-related potentials (ERPs) to facial expressions depend on cognitive load during the expectation phase

Previous studies have shown that event-related potentials (ERPs) to facial expressions are modulated by expectation (congruency) and that the ERP effects of expectation congruency are altered by cognitive tasks during the expectation phase. However, it is as yet unknown whether the congruency ERP effects can be modulated by the amount of cognitive load during the expectation phase. To address this question, electroencephalogram (EEG) was acquired when participants viewed fearful and neutral facial expressions. Before the presentation of facial expressions, a cue indicating the expression of a face and subsequently, an expectation interval without any cues were presented. Facial expressions were congruent with the cues in 75% of all trials. During the expectation interval, participants had to solve a cognitive task, in which several letters were presented for target letter detection. The letters were all the same under low load, but differed under high load. Event-related potential (ERP) results showed that the amount of cognitive load during the expectation phase altered the congruency effect in N2 and EPN amplitudes for fearful faces. Congruent as compared to incongruent fearful expressions elicited larger N2 and smaller EPN amplitudes under low load, but these congruency effects were not observed under high load. For neutral faces, a congruency effect in late positive potential (LPP) amplitudes was modulated by cognitive load during the expectation phase. The LPP was more positive for incongruent as compared to congruent faces under low load, but the congruency effect was not evident under high load. The findings indicate that congruency effects on ERPs are modulated by the amount of cognitive load the expectation phase and that this modulation is altered by facial expression.

Temporal Expectation Weights Visual Signals Over Auditory Signals

Temporal expectation is a process by which people use temporally structured sensory information to explicitly or implicitly predict the onset or duration of future events. Temporal Expectation has been shown to influence responses to stimuli in visual, auditory, and tactile modalities, but less is known about the effects of temporal expectation on crossmodal processing. Because timing plays an important role in crossmodal interaction, we investigated how temporal expectation influenced auditory-visual interaction, using an auditory-visual congruity effect as a measure of crossmodal interaction. On each trial, participants received a modality cue indicating whether a target letter, B or D, would be presented auditorily or visually. The task was to identify the letter in the cued modality as rapidly and as accurately as possible. Each target was simultaneously accompanied by either a congruent or an incongruent letter presented through the other modality. Temporal expectation was block-wise manipulated by varying the relative probability of a stimulus appearing at a short or long interval after the modality cue. In the short-interval-expected block, the short interval was used 80% of the time and the long interval was used 20% of the time. In the long-interval-expected block, the probabilities were reversed. For auditory identification, an incongruent visual stimulus produced stronger interference when the bimodal stimulus was presented with expected than with unexpected timing. In contrast, for visual identification, an incongruent auditory stimulus produced weaker interference when the bimodal stimulus was presented with expected than with unexpected timing. The fact that temporal expectation made visual distracters more potent and visual targets less susceptible to auditory interference suggests that temporal expectation increases perceptual weight on visual signals. Meeting abstract presented at VSS 2016

Development of crowding: A new chart to measure crowding without requiring good fixation

Evidence from the periphery, strabismic amblyopia, apperceptive agnosia, and posterior cortical atrophy show an association between the critical spacing of crowding and neural density, the number of cortical neurons per deg^2 responding to a given eye (see Strappini, et al., submitted to Cortex). Evidence for reduction in the critical spacing of crowding in development could be misleading if it's merely a result of improved fixation with age. David Regan introduced a repeated-letter acuity test, to measure acuity without requiring good fixation. We use a variant of that test here to measure acuity, and we introduce a new repeated-letter crowding test to measure crowding without requiring good fixation. Regan's repeated-letter acuity test repeats the target letter AAAAA. Our repeated-letter crowding test alternates two targets ABABABABAB and the observer is asked to report both targets. For a balanced design, we create a dual-target repeated-letter acuity test AAAAABBBBB, and ask the observer to report both targets. We also use conventional single-target tests for acuity A and crowding XAX. Center-to-center letter spacing was always 1.4 times the letter size, and we used QUEST to adjust size (or spacing) to threshold, allowing the other parameter to co-vary. Pilot data on three normally sighted students shows excellent agreement between threshold size & spacing measured with single vs. repeated targets: size 0.054±1 vs. 0.050±4 deg & spacing 0.083±6 vs. 0.081±10 deg (M±SE). Conclusions: 1. Repeating the targets does not change threshold size and spacing in normally sighted adult observers with good fixation. 2. Repeating a single letter does not produce crowding, presumably because jumbling the target and flanker features yields the same features as a target alone. 3. This chart is a promising way to measure the development of foveal crowding even in patients or children with poor fixation. Meeting abstract presented at VSS 2016

Social Groups Prioritize Selective Attention to Faces: How Social Identity Shapes Distractor Interference.

Human faces automatically attract visual attention and this process appears to be guided by social group memberships. In two experiments, we examined how social groups guide selective attention toward in-group and out-group faces. Black and White participants detected a target letter among letter strings superimposed on faces (Experiment 1). White participants were less accurate on trials with racial out-group (Black) compared to in-group (White) distractor faces. Likewise, Black participants were less accurate on trials with racial out-group (White) compared to in-group (Black) distractor faces. However, this pattern of out-group bias was only evident under high perceptual load—when the task was visually difficult. To examine the malleability of this pattern of racial bias, a separate sample of participants were assigned to mixed-race minimal groups (Experiment 2). Participants assigned to groups were less accurate on trials with their minimal in-group members compared to minimal out-group distractor faces, regardless of race. Again, this pattern of out-group bias was only evident under high perceptual load. Taken together, these results suggest that social identity guides selective attention toward motivationally relevant social groups—shifting from out-group bias in the domain of race to in-group bias in the domain of minimal groups—when perceptual resources are scarce.

Perceptual Learning in Children With Infantile Nystagmus: Effects on 2D Oculomotor Behavior.

To determine changes in oculomotor behavior after 10 sessions of perceptual learning on a letter discrimination task in children with infantile nystagmus (IN). Children with IN (18 children with idiopathic IN and 18 with oculocutaneous albinism accompanied by IN) aged 6 to 11 years were divided into two training groups matched on diagnosis: an uncrowded training group (n = 18) and a crowded training group (n = 18). Target letters always appeared briefly (500 ms) at an eccentric location, forcing subjects to quickly redirect their gaze. Training occurred twice per week for 5 consecutive weeks (3500 trials total). Norm data and test-retest values were collected from children with normal vision (n = 11). Outcome measures were: nystagmus characteristics (amplitude, frequency, intensity, and the expanded nystagmus acuity function); fixation stability (the bivariate contour ellipse area and foveation time); and saccadic eye movements (latencies and accuracy) made during a simple saccade task and a crowded letter-identification task. After training, saccadic responses of children with IN improved on the saccade task (latencies decreased by 14 ± 4 ms and gains increased by 0.03 ± 0.01), but not on the crowded letter task. There were also no training-induced changes in nystagmus characteristics and fixation stability. Although children with normal vision had shorter latencies in the saccade task (47 ± 14 ms at baseline), test-retest changes in their saccade gains and latencies were almost equal to the training effects observed in children with IN. Our results suggest that the improvement in visual performance after perceptual learning in children with IN is primarily due to improved sensory processing rather than improved two-dimensional oculomotor behavior.

Cardiac cycle time effects on selection efficiency in vision.

The effect of cardiac cycle time on attentional selection was investigated in an experiment in which participants classified target letters in a visual selection task. Stimulus onsets were aligned to the R wave of the electrocardiogram and stimuli presented either during the ventricular systole or diastole. Selection efficiency was operationalized as difference in target selection performance under conditions of homogeneous and heterogeneous distractors. Differences in performance (i.e., the impact selection difficulty had on the ability to select the target) were attenuated for stimuli presented during the ventricular systole compared to the diastole. Increased baroafferent signal transmission during the systole appears to reduce interference of highly distracting stimuli on visual selection efficiency.

Движения глаз в ходе спонтанного и контролируемого обнаружения слов в больших буквенных массивах

Целью работы было изучение возможностей и ограничений нисходящих влияний на обработку зрительных стимулов на материале задачи зрительного поиска букв и слов в случайных рядах букв. В наших недавних экспериментах было показано, что присутствие слов в буквенных массивах, в которых наблюдатель решает задачу поиска букв, не влияет на продуктивность решения этой задачи вне зависимости от того, замечает ли испытуемый слова. Мы установили, что спонтанное выделение слов и их произвольное отыскание в соответствии с инструкцией задействуют разные стратегии поиска, меняющие характер движений глаз. Спонтанное обнаружение слов при поиске букв не имеет значимых глазодвигательных коррелятов, в то время как контролируемый поиск слов увеличивает число фиксаций как в пределах слов, так и между ними. В дополнительном исследовании мы показали, что знание категориальной принадлежности слов не помогает испытуемым в выполнении задания на поиск слов; по всей видимости, в этом случае сначала происходит установление границ и выделение слов в стимульном материале и только затем процесс их категоризации. Таким образом, к обнаружению слов в буквенных массивах могут приводить, по крайней мере, два различных процесса: спонтанного обнаружения слова, опосредованный кодированием отдельных букв, и контролируемого выделения слова, опосредованный обработкой информации о слове как о целостной перцептивной единице.

The Impact of Childhood Anxiety on Processes of Attentional Executive Control in the Presence of Emotional Face Distractors

Anxiety interferes with executive control of attention (ECA), especially in the context of emotional information. Previous research suggests that temperamental differences in self-regulation might modulate these effects. The present research examined the association between trait anxiety and temperamental self-regulation on ECA processes, in the context of positive and threatening distractors in a sample of primary school children. We designed a computerized Emotional letter discrimination task that required both inhibitory and set shifting processes. Emotional faces distractors were displayed one at a time during a primary letter discrimination task. To assess inhibition, our task contained compatible trials (the target letter was flanked by distractor letter that had the same identity as the target) and incompatible trials (the target letter was flanked by distractor letter that had the opposite identity). The results showed that higher levels of anxiety were associated with increased reaction times to discriminate target letters during incompatible trials in the presence of happy distractors. In addition, lower levels of temperamental self-regulation were related to increased reaction times in the presence of angry distractors during incompatible trials. These findings provide empirical evidence for an association between increased child anxiety and lower self-regulation on the executive control of attention in the context of emotional distracting information.

Attachment Representation Moderates the Influence of Emotional Context on Information Processing.

The induction of emotional states has repeatedly been shown to affect cognitive processing capacities. At a neurophysiological level, P3 amplitude responses that are associated with attention allocation have been found to be reduced to task-relevant stimuli during emotional conditions as compared to neutral conditions suggesting a draining impact of emotion on cognitive resources. Attachment theory claims that how individuals regulate their emotions is guided by an internal working model (IWM) of attachment that has formed early in life. While securely attached individuals are capable of freely evaluating their emotions insecurely attached ones tend to either suppress or heighten the emotional experience in a regulatory effort. To explore how attachment quality moderates the impact of emotional contexts on information processing event-related potentials (ERPs) in 41 individuals were assessed. Subjects were instructed to detect neutral target letters within an oddball paradigm. Various images taken from the International Affective Picture System (IAPS) served as background pictures and represented negative, positive and neutral task-irrelevant contexts. Attachment representation was assessed using the Adult Attachment Interview (AAI) and individuals were assigned to one of three categories (secure, insecure-dismissing, insecure-preoccupied). At a behavioral level, the study revealed that negative emotionally conditions were associated with the detection of less target stimuli in insecure-dismissing subjects. Accordingly, ERPs yielded reduced P3 amplitudes in insecure-dismissing subjects when given a negative emotional context. We interpret these findings in terms of less sufficient emotion regulation strategies in insecure-dismissing subjects at the cost of accurate behavioral performance. The study suggests that attachment representation differentially moderates the relationship between emotional contexts and information processing most evident in insecure-dismissing subjects.

Effects of flanker type and position on foveal letter recognition

Our ability to identify a foveally viewed letter at resolution threshold reduces when flankers are placed at a certain distance from it, compared to when it is presented on its own. In this study, we investigated how type and position of flankers influences foveal letter recognition. We measured participants’ performance to identify unflanked Sheridan-Gardiner letters (A, H, O, U, T, V or X), using a seven-alternative-forced-choice paradigm with the method of constant stimuli to obtain 80-90% correct response. Performance was measured again to identify a target letter in the presence of different flanker types. Flankers were bars and letters (placed either to the left and right of the target, above and below the target or on four sides of the target), and a surrounding box. Separation between the target letter and flankers varied between zero (abutting) and ten stroke widths (two letter sizes). For all flanker types, separation between the target ad the flankers significantly influenced performance (all p < 0.0001). Flankers abutting the target and at separation of one stroke width caused the largest reduction in performance, regardless of flanker type. For bar flankers, the largest drop in performance (up to 50 percent) occurred with bars placed on all four sides of the target. For letter flankers, flankers placed above and below the target reduced performance as much as four surrounding flankers. At separation of one stroke width, flanking letters and bars caused a further 10% reduction in performance than a surrounding box. Our results would have significant implications on the design of crowded visual acuity charts, especially those that are available on the market, which have different crowding features between them.

Acute Stress and Perceptual Load Consume the Same Attentional Resources: A Behavioral-ERP Study.

Stress and perceptual load affect selective attention in a paradoxical manner. They can facilitate selectivity or disrupt it. This EEG study was designed to examine the reciprocal relations between stress, load and attention. Two groups of subjects, one that performed the Trier Social Stress Test (TSST), and a control group, were asked to respond to a target letter under low and high perceptual load in the absence or presence of a distractor. In the control group, the distractor increased response times (RTs) for high and low load. In the TSST group, distractor increased RTs under low load only. ERPs showed that distractor’s presentation attenuated early visual P1 component and shortened its latency. In the TSST group, distractor reduced P1 component under high load but did not affect its latency. Source localization demonstrated reduced activation in V1 in response to distractors presence in the P1 time window for the TSST group compared to the control group. A behavioral replication revealed that in the TSST group distractors were less perceived under high load. Taken together, our results show that stress and perceptual load affect selectivity through the early stages of visual processing and might increase selectivity in a manner that would block conscious perception of irrelevant stimuli.

The Missing-Phoneme Effect in Aural Prose Comprehension

When participants search for a target letter while reading for comprehension, they miss more instances if the target letter is embedded in frequent function words than in less frequent content words. This phenomenon, called the missing-letter effect, has been considered a window on the cognitive mechanisms involved in the visual processing of written language. In the present study, one group of participants read two texts for comprehension while searching for a target letter, and another group listened to a narration of the same two texts while listening for the target letter’s corresponding phoneme. The ubiquitous missing-letter effect was replicated and extended to a missing-phoneme effect. Item-based correlations between the reading and listening tasks were high, which led us to conclude that both tasks involve cognitive processes that reading and listening have in common and that both processes are rooted in psycholinguistically driven allocation of attention.

The Impact of Perceptual Load on the Non-Conscious Processing of Fearful Faces.

Emotional stimuli can be processed without consciousness. In the current study, we used event-related potentials (ERPs) to assess whether perceptual load influences non-conscious processing of fearful facial expressions. Perceptual load was manipulated using a letter search task with the target letter presented at the fixation point, while facial expressions were presented peripherally and masked to prevent conscious awareness. The letter string comprised six letters (X or N) that were identical (low load) or different (high load). Participants were instructed to discriminate the letters at fixation or the facial expression (fearful or neutral) in the periphery. Participants were faster and more accurate at detecting letters in the low load condition than in the high load condition. Fearful faces elicited a sustained positivity from 250 ms to 700 ms post-stimulus over fronto-central areas during the face discrimination and low-load letter discrimination conditions, but this effect was completely eliminated during high-load letter discrimination. Our findings imply that non-conscious processing of fearful faces depends on perceptual load, and attentional resources are necessary for non-conscious processing.

Spatio-temporal properties of letter crowding.

Crowding between adjacent letters has been investigated primarily as a spatial effect. The purpose of this study was to investigate the spatio-temporal properties of letter crowding. Specifically, we examined the systematic changes in the degradation effects in letter identification performance when adjacent letters were presented with a temporal asynchrony, as a function of letter separation and between the fovea and the periphery. We measured proportion-correct performance for identifying the middle target letter in strings of three lowercase letters at the fovea and 10° in the inferior visual field, for a range of center-to-center letter separations and a range of stimulus onset asynchronies (SOA) between the target and flanking letters (positive SOAs: target preceded flankers). As expected, the accuracy for identifying the target letters reduces with decreases in letter separation. This crowding effect shows a strong dependency on SOAs, such that crowding is maximal between 0 and ∼100 ms (depending on conditions) and diminishes for larger SOAs (positive or negative). Maximal crowding does not require the target and flanking letters to physically coexist for the entire presentation duration. Most importantly, crowding can be minimized even for closely spaced letters if there is a large temporal asynchrony between the target and flankers. The reliance of letter identification performance on SOAs and how it changes with letter separations imply that the crowding effect can be traded between space and time. Our findings are consistent with the notion that crowding should be considered as a spatio-temporal, and not simply a spatial, effect.

Decomposing Self-Control: Individual Differences in Goal Pursuit Despite Interfering Aversion, Temptation, and Distraction.

Self-control can be defined as the ability to exert control over ones impulses. Currently, most research in the area relies on self-report. Focusing on attentional control processes involved in self-control, we modified a spatial selective attentional cueing task to test three domains of self-control experimentally in one task using aversive, tempting, and neutral picture-distractors. The aims of the study were (1) to investigate individual differences in the susceptibility to aversive, tempting, and neutral distraction within one paradigm and (2) to test the association of these three self-control domains to conventional measures of self-control including self-report. The final sample consisted of 116 participants. The task required participants to identify target letters “E” or “F” presented at a cued target location while the distractors were presented. Behavioral and eyetracking data were obtained during the performance of the task. High task performance was encouraged via monetary incentives. In addition to the attentional self-control task, self-reported self-control was assessed and participants performed a color Stroop task, an unsolvable anagram task and a delay of gratification task using chocolate sweets. We found that aversion, temptation, and neutral distraction were associated with significantly increased error rates, reaction times and gaze pattern deviations. Overall task performance on our task correlated with self-reported self-control ability. Measures of aversion, temptation, and distraction showed moderate split-half reliability, but did not correlate with each other across participants. Additionally, participants who made a self-controlled decision in the delay of gratification task were less distracted by temptations in our task than participants who made an impulsive choice. Our individual differences analyses suggest that (1) the ability to endure aversion, resist temptations and ignore neutral distractions are independent of each other and (2) these three domains are related to other measures of self-control.

Irrelevant learned reward associations disrupt voluntary spatial attention.

Attention can be guided involuntarily by physical salience and by non-salient, previously learned reward associations that are currently task-irrelevant. Attention can be guided voluntarily by current goals and expectations. The current study examined, in two experiments, whether irrelevant reward associations could disrupt current, goal-driven, voluntary attention. In a letter-search task, attention was directed voluntarily (i.e., cued) on half the trials by a cue stimulus indicating the hemifield in which the target letter would appear with 100 % accuracy. On the other half of the trials, a cue stimulus was presented, but it did not provide information about the target hemifield (i.e., uncued). On both cued and uncued trials, attention could be involuntarily captured by the presence of a task-irrelevant, and physically non-salient, color, either within the cued or the uncued hemifield. Importantly, one week prior to the letter search task, the irrelevant color had served as a target feature that was predictive of reward in a separate training task. Target identification accuracy was better on cued compared to uncued trials. However, this effect was reduced when the irrelevant, and physically non-salient, reward-associated feature was present in the uncued hemifield. This effect was not observed in a second, control experiment in which the irrelevant color was not predictive of reward during training. Our results indicate that involuntary, value-driven capture can disrupt the voluntary control of spatial attention.

Distracted by pleasure: Effects of positive versus negative valence on emotional capture under load.

We report 3 experiments examining the effects of positive versus negative valence and perceptual load in determining attention capture by irrelevant emotional distractors. Participants performed a letter search task searching for 1 of 2 target letters (X or N) in conditions of either low perceptual load (circular nontarget letters) or high perceptual load (angular nontarget letters that are similar to the target letters). On 25% of the trials an irrelevant emotional distractor was presented at the display center and participants were instructed to ignore it. The distractor stimulus was either positive or negative and was selected from 3 different classes: IAPS pictures of erotica or mutilated bodies (Experiment 1), happy or angry faces (Experiment 2), and faces associated with gain or loss in a prior value-learning phase involving a betting game (Experiment 3). The results showed a consistent pattern of interaction of load and valence across the 3 experiments. Irrelevant emotional distractors produced interference effects on search reaction time (RT) in conditions of low load, with no difference between negative and positive valence. High perceptual load, however, consistently reduced interference from the negative-valence distractors, but had no effect on the positive-valence distractors. As these results were consistently found across 3 different categories of emotional distractors, they suggest the general conclusion that attentional capture by irrelevant emotional distractors depends on both their valence and the level of perceptual load in the task and highlight the special status of distractors associated with pleasure.

Top-Down Processes Override Bottom-Up Interference in the Flanker Task

Distractor interference in the flanker task is commonly viewed as an outcome of unintentional, involuntary processing, a by-product of attention-controlled processing of the target. An important implication of this notion is that the distractors are not subjected to top-down processing of their own. We tested this idea in a modified version of the flanker task, in which letter targets (S or O) were sometimes flanked by ambiguous distractors (a character that could be S or 5 or one that could be O or 0). Distractor interference was dependent on participants’ expectations regarding the category of the distractors (i.e., letters or digits). For example, the O-0 distractor interfered with responding to S when it was perceived as a letter, but not when it was perceived as a digit. Hence, participants applied top-down processing to the peripheral distractors independently of the top-down processing applied to the targets. The fact that to-be-ignored peripheral distractors were processed to such a high level raises questions regarding the fundamental differences between target and distractor processing, and the quality of attentional filtering.