Letter Identification Task Research Articles

The Automaticity of Affordance of Dangerous Object.

Objects observation automatically elicits the activation of a reach-to-grasp response specifically directed to interact with the object, which is termed affordance. Murphy, van Velzen, and de Fockert (2012) found that only when an irrelevant object receives sufficient attention, it can potentiate an action. However, it remains unclear whether the dangerous object would afford an action when it receives insufficient attention. In this study, we manipulated the perceptual load in a letter identification task. Participants were required to identify a target letter with the right or left hand while ignoring a neutral or dangerous graspable object. The target letter was presented either on its own (low perceptual load), alongside five non-target letters (high load), or alongside eight non-target letters (super high load). Under the low perceptual load, for both neutral and dangerous object, responses were faster when the action afforded by the ignored object was congruent (vs. incongruent) with the current target response (t(27) = 4.44, p < .001; t(27) = 7.99, p < .001, respectively). However, during the high perceptual load, for dangerous object, responses were slower when the action afforded by the ignored object was congruent (vs. incongruent) with the current target response (t(27) = 4.97, p < .001). There was not any effect for both neutral object and dangerous object under super high perceptual load. These results suggest the affordance of dangerous object is also sensitive to the perceptual load. An irrelevant dangerous object can't potentiate an action if it receives insufficient attention.

Comparison of Psychophysiological and Dual-Task Measures of Listening Effort

We wished to make a comparison of psychophysiological measures of listening effort with subjective and dual-task measures of listening effort for a diotic-dichotic-digits and a sentences-in-noise task. Three groups of young adults (18-38 years old) with normal hearing participated in three experiments: two psychophysiological studies for two different listening tasks and a dual-task measure for a sentences-in-noise task. Psychophysiological variables included skin conductance, heart-rate variability, and heart rate; the dual-task measure was a letter-identification task. Heart-rate variability was quantified with the difference from baseline for the normalized standard deviation of R to R. Heart-rate variability differences from baseline were greater for increased task complexity and for poorer signal-to-noise ratios (SNRs). The dual-task measure of listening effort also increased for sentences presented at a +5 dB SNR compared with a +15 dB SNR. Skin conductance was elevated for greater task complexity only, and similar across noise conditions. None of these measures were significantly correlated with subjective measures of listening effort. Heart-rate variability appears to be a robust psychophysiological indicator of listening effort, sensitive to both task complexity and SNR. This sensitivity to SNR was similar to a dual-task measure of listening effort.

Gradual development of temporal attention in letter identification and motion judgment tasks

Gradual development of temporal attention in letter identification and motion judgment tasks

Attentional switches and dual-task interference.

In four experiments, we studied the time course of interference between detection of an oddball orientation target (OT) in an 8-item circular search display, and identification of a letter target (LT) in a central stream of distractor letters. Dual-task performance for different temporal lags between targets was compared to single-task performance. When the LT preceded the OT, dual-task performance levels were reduced at short inter-target intervals of 0 and 166 ms; when the OT preceded the LT, the dual-task interference was unexpectedly stronger and lasted for up to 500 ms. Resource competition due to temporally overlapping target processing cannot account for this result, because the feature search task is easier than the letter identification task, and therefore would have generated less interference when presented first. Two alternative explanations were explored. First, by manipulating the spatial inter-target distance, we investigated to what degree there is a penalty associated with directing the attentional window from a large object (the search display) to a smaller object (the central letter stream). Second, by varying the duration of the OT and subsequent mask, we studied whether the interference was caused by the difficulty of disengaging attention from the search display. Results support this second explanation and thus indicate that switching attention to the letter stream is hampered by the continuing presence of (masked) search display items. This result shows that attentional effects may play a major role in dual-task execution and can easily obscure interference due to other factors such as resource competition.

Does attention speed up processing? Decreases and increases of processing rates in visual prior entry.

Selective visual attention improves performance in many tasks. Among others, it leads to "prior entry"--earlier perception of an attended compared to an unattended stimulus. Whether this phenomenon is purely based on an increase of the processing rate of the attended stimulus or if a decrease in the processing rate of the unattended stimulus also contributes to the effect is, up to now, unanswered. Here we describe a novel approach to this question based on Bundesen's Theory of Visual Attention, which we use to overcome the limitations of earlier prior-entry assessment with temporal order judgments (TOJs) that only allow relative statements regarding the processing speed of attended and unattended stimuli. Prevalent models of prior entry in TOJs either indirectly predict a pure acceleration or cannot model the difference between acceleration and deceleration. In a paradigm that combines a letter-identification task with TOJs, we show that indeed acceleration of the attended and deceleration of the unattended stimuli conjointly cause prior entry.

Metamorphopsia and letter recognition.

Acuity is the most commonly used measure of visual function, and reductions in acuity are associated with most eye diseases. Metamorphopsia--a perceived distortion of visual space--is another common symptom of visual impairment and is currently assessed qualitatively using Amsler (1953) charts. In order to quantify the impact of metamorphopsia on acuity, we measured the effect of physical spatial distortion on letter recognition. Following earlier work showing that letter recognition is tuned to specific spatial frequency (SF) channels, we hypothesized that the effect of distortion might depend on the spatial scale of visual distortion just as it depends on the spatial scale of masking noise. Six normally sighted observers completed a 26 alternate forced choice (AFC) Sloan letter identification task at five different viewing distances, and the letters underwent different levels of spatial distortion. Distortion was controlled using spatially band-pass filtered noise that spatially remapped pixel locations. Noise was varied over five spatial frequencies and five magnitudes. Performance was modeled with logistic regression and worsened linearly with increasing distortion magnitude and decreasing letter size. We found that retinal SF affects distortion at midrange frequencies and can be explained with the tuning of a basic contrast sensitivity function, while object-centered distortion SF follows a similar pattern of letter object recognition sensitivity and is tuned to approximately three cycles per letter (CPL). The interaction between letter size and distortion makes acuity an unreliable outcome for metamorphopsia assessment.

Attentional capture by dynamic cues.

Attention orients to an object that abruptly onsets, because the object's appearance alters the visual scene. In this report, the question was whether there would, similarly, be attentional prioritization of an existing object that changes its dynamic status. Attention may be deployed immediately to the object because its new dynamic status, potentially, also could alter the visual environment. This report focused on the capture capacity of an object--made up of four spots--that abruptly began rotating, thereby endowing it with two dynamic features: motion-onset, apparent when the object transitioned from stationary to moving, and its specific motion trajectory. Because the rotating spots were irrelevant to the main letter-identification task, there ought not to be top-down attentional orienting to them. We asked two questions: (a) whether the rotating object captures attention automatically, and (b) whether both its dynamic features contribute to attentional capture. Four experiments were reported. The observer's attentional set was manipulated by varying, across experiments, the target's diagnostic feature. We examined how the different attentional sets modulated capture. The results showed that the rotating object only succeeded in capturing attention when the attentional system was set to monitor dynamic features.

Effects of Age and Cardiovascular Disease on Selective Attention

In order to study the effect of normal aging and cardiovascular disease on selective attention, a letter-identification task was proposed to younger and older healthy adults as well as patients with a recent myocardial infarction or a recent coronary artery bypass grafting. Participants had to detect either a big stimulus or a small one surrounded by flanking letters. The stimuli were displayed horizontally, either in the left (LVF) or in the right visual field (RVF). The interaction between the type of stimulus and the hemifield of presentation reached significance in all groups except in patients who underwent a coronary artery bypass. Only young normal adults showed the expected significant RVF advantage when detecting big stimuli and an LVF advantage when detecting small stimuli surrounded by flankers. In older control adults and in patients with myocardial infarction, the RVF advantage for the condition with selective attention vanished. In patients who underwent a coronary artery bypass, reaction times were increased and no hemispheric specialization for selective attention emerged. The results are discussed with regard to the hypothesis of a Hemispheric Asymmetry Reduction in Older Adults (HAROLD model) and to the presence of cognitive dysfunction consecutive to cardiovascular disease.

The classical TDT perceptual learning is mostly temporal learning

The seminal study on perceptual learning of TDT (a texture discrimination task) has greatly shaped the field of perceptual learning up to the present time. However, here we demonstrate that this classic learning mostly involves temporal learning, rather than texture discrimination learning. Specifically, observers first practiced a letter identification task with backward masking to saturate the potential temporal learning of target-mask separation in TDT learning before they practiced the backward-masked TDT task directly. The temporal learning accounted for most of the overall TDT improvement, indicating TDT learning being mostly temporal learning. Meanwhile, the location specificity of TDT learning may be interpreted as temporal learning being confined to the trained location with conventional training because learning became mostly location invariant with double training. These results provide a new context to interpret the existing TDT brain imaging data aimed at understanding the neural mechanisms of perceptual learning.

Attentional Requirements on Feature Search Are Modulated by Stimulus Properties

We report a series of dual-task experiments, in which a rapid serial visual presentation (RSVP) task was combined with a visual search task. Orientation, motion, and color were used as the defining target features in the search task. Lag between target onsets was manipulated and interference between the two tasks was quantified by measuring detection scores for the search task as a function of lag. While simultaneous performance of an orientation detection task with an RSVP letter identification task resulted in a performance decrease for lags up to 320 ms, no such decrease was detected for highly salient motion- and color-defined targets. Subsequently, detectability of the motion and color feature was matched to that of the orientation-feature resulting in the reintroduction of a (smaller) performance decrease, but only during simultaneous performance (lag 0 ms). The results suggest that there are two causes for the impaired search performance occurring when a feature search task is combined with an RSVP task. The first is short-lasting interference probably due to attentional competition; the second, which plays a role only when targets for both tasks share features, is interference that may be attributed to a central processing bottleneck.

Attentional capture by the onset and offset of motion signals outside the spatial focus of attention

The present study examined whether participants were able to ignore a task-irrelevant commencement or cessation of optic flow while they were engaging in a letter-identification task, as claimed by adherents of the view that attentional set determines deployment of attention, or whether irrelevant events would capture attention regardless of observers' attentional set, as claimed by adherents of a broad range of views emphasizing the behavioral urgency of stimulus motion. Observers identified a green letter in a central rapid stream of heterogeneously colored nontargets. A completely task-irrelevant optic flow occurred in the periphery. If attentional deployment were governed by a top-down attentional set, the letter identification would be unaffected by the temporal change in the optic flow. The results reflected attentional capture by commencement or cessation of optic flow, which is inconsistent with the top-down view. When the peripheral dots expanded at various speeds before onset of the target, identification was impaired relative to when no motion occurred. Mere commencement or cessation of motion was sufficient to produce the capture effect. Qualitative (commencement or cessation) rather than quantitative changes (acceleration or deceleration) of the motion display were critical for the occurrence of attentional capture. We conclude that salient discontinuities in optic flow induce attentional capture when observers search for a feature in a different stimulus domain, an idea implying a unique role for of expanding global motion in the deployment of visual attention.

Masked repetition priming of letter-in-string identification: An ERP investigation

In a post-cued letter identification task, participants were presented with 7-letter nonword target stimuli that were formed of a random string of consonants (DCMFPLR) or a pronounceable sequence of consonants and vowels (DAMOPUR). Targets were preceded by briefly presented pattern-masked primes that could be the same sequence of letters as the target, composed of seven different letters, or sharing either the first or last five letters of the target. There was some evidence for repetition priming effects that were independent of target type in an early component, the N/P150, thought to reflect the mapping of visual features onto letter representations, and that is insensitive to orthographic structure. Following this, pronounceable nonwords showed significantly greater repetition priming effects than consonant strings, in line with the behavioral results. Initial versus final overlap only started to influence target processing at around 200–250ms post-target onset, at about the same time as the effects of target type emerged. The results are in line with a model where the initial parallel mapping of visual features onto a location-specific orthographic code is followed by the subsequent activation of location-invariant orthographic and phonological codes.

Learning to Identify Near-Acuity Letters, either with or without Flankers, Results in Improved Letter Size and Spacing Limits in Adults with Amblyopia

Amblyopia is a developmental abnormality that results in deficits for a wide range of visual tasks, most notably, the reduced ability to see fine details, the loss in contrast sensitivity especially for small objects and the difficulty in seeing objects in clutter (crowding). The primary goal of this study was to evaluate whether crowding can be ameliorated in adults with amblyopia through perceptual learning using a flanked letter identification task that was designed to reduce crowding, and if so, whether the improvements transfer to untrained visual functions: visual acuity, contrast sensitivity and the size of visual span (the amount of information obtained in one fixation). To evaluate whether the improvements following this training task were specific to training with flankers, we also trained another group of adult observers with amblyopia using a single letter identification task that was designed to improve letter contrast sensitivity, not crowding. Following 10,000 trials of training, both groups of observers showed improvements in the respective training task. The improvements generalized to improved visual acuity, letter contrast sensitivity, size of the visual span, and reduced crowding. The magnitude of the improvement for each of these measurements was similar in the two training groups. Perceptual learning regimens aimed at reducing crowding or improving letter contrast sensitivity are both effective in improving visual acuity, contrast sensitivity for near-acuity objects and reducing the crowding effect, and could be useful as a clinical treatment for amblyopia.

Lingual tactile acuity and food texture preferences among children and their mothers

Despite anecdotal reports of children being more sensitive to texture than adults, and of texture being one of the main drivers of food aversions, there is a paucity of scientific knowledge on the influence of texture perception on food choice in children. The primary goals of this study were to assess the use of a modified letter-identification task to study lingual tactile acuity, one aspect of oral sensitivity, in children and to examine age-related differences in sensitivity. The secondary goal was to explore whether lingual tactile acuity and age relate to various measures of food choice and preference. To this end, children 7–10years old (31 girls, 21 boys) and their mothers were tested using identical procedures. To assess lingual tactile acuity, children and mothers were asked to use the tips of their tongues to identify raised alphabetical letters of varying size (2.5–8.0mm) on Teflon strips. To relate lingual tactile acuity to food texture preferences, a forced-choice questionnaire assessed preferences for foods similar in flavor but different in texture (e.g., smooth versus crunchy peanut butter). Children were able to complete the lingual acuity task as well as their mothers and took less time to assess each letter stimulus (p<0.001); however, there were no age-related differences in lingual acuity (p=0.14). Age, but not lingual acuity, related to food texture preferences: mothers preferred harder foods (p<0.001) and those containing more particles (p<0.04) than did children, although children’s preferences became more adult-like with increasing age. The availability of a rapid, child-friendly method for assessing oral sensitivity opens up new possibilities of examining differences in oral tactile perceptions across the life span. That food preferences changed with age and were not related to oral sensitivity underscores the fact that factors such as family food practices, culture and experience have a significant impact on children’s food texture preferences.

Gender differences revealed in the right posterior temporal areas during Navon letter identification tasks

Gender differences in temporo-spectral EEG patterns during verbal cognitive performance are poorly understood. The aim of the present study was to examine whether the event-related dynamics of EEG differ between genders during the performance of Navon letter identification tasks (NLITs). To this end, the EEG patterns of 40 subjects were recorded during the NLIT performance. We compared behavioral outcomes, event-related temporo-spectral dynamics, and source distribution of neural oscillations within cortical regions of male and female subjects. We found that male subjects exhibited greater induced neural activities than female subjects in right temporo-parietal areas at theta and alpha frequency bands. Source imaging for the time ranges at which maximal gender differences were observed revealed gender-dependent estimated current densities in the right posterior temporal regions. These gender differences can be explained by the existence of distinct, gender-specific hemispheric specialization. Thus, gender differences should be considered during behavioral tasks and electrophysiological measurements.

Perceptual Learning Reduces Crowding in Amblyopia and in the Normal Periphery

Amblyopia is a developmental visual disorder of cortical origin, characterized by crowding and poor acuity in central vision of the affected eye. Crowding refers to the adverse effects of surrounding items on object identification, common only in normal peripheral but not central vision. We trained a group of adult human amblyopes on a crowded letter identification task to assess whether the crowding problem can be ameliorated. Letter size was fixed well above the acuity limit, and letter spacing was varied to obtain spacing thresholds for central target identification. Normally sighted observers practiced the same task in their lower peripheral visual field. Independent measures of acuity were taken in flanked and unflanked conditions before and after training to measure crowding ratios at three fixed letter separations. Practice improved the letter spacing thresholds of both groups on the training task, and crowding ratios were reduced after posttest. The reductions in crowding in amblyopes were associated with improvements in standard measures of visual acuity. Thus, perceptual learning reduced the deleterious effects of crowding in amblyopia and in the normal periphery. The results support the effectiveness of plasticity-based approaches for improving vision in adult amblyopes and suggest experience-dependent effects on the cortical substrates of crowding.

Performance Dip in Motor Response Induced by Task-Irrelevant Weaker Coherent Visual Motion Signals

The Performance Dip is a newly characterized behavioral phenomenon, where, paradoxically, a weaker task-irrelevant visual stimulus causes larger disturbances on the accuracy of a main letter identification task than a stronger stimulus does. Understanding mechanisms of the Performance Dip may provide insight into unconsciousness behavior. Here, we investigated the generalization of the Performance Dip. Specifically, we tested whether the Performance Dip occurs in a motion-related Simon task, and if so, whether the Performance Dip involves the same brain region, that is, the dorsolateral prefrontal cortex (DLPFC), previously implicated in the Performance Dip, or the supplementary motor area (SMA) and pre-SMA, implicated in a motion-related Simon Task. Subjects made manual directional responses according to the color of stochastic moving dots while ignoring the global direction of moving dots, which could be either congruent or incongruent to the response appropriate to the main task. We found that weak incongruent task-irrelevant stimuli caused a Performance Dip, in which the SMA and pre-SMA, rather than DLPFC, played critical roles. Our results suggest a possible common brain mechanism across different neural circuits, in which weak, but not strong, task-irrelevant information is free from inhibition and intrudes into neural circuits relevant to the main task.

Attentional Modulation of Temporal Contrast Sensitivity in Human Vision

Recent psychophysical studies have shown that attention can alter contrast sensitivities for temporally broadband stimuli such as flashed gratings. The present study examined the effect of attention on the contrast sensitivity for temporally narrowband stimuli with various temporal frequencies. Observers were asked to detect a drifting grating of 0–40 Hz presented gradually in the peripheral visual field with or without a concurrent letter identification task in the fovea. We found that removal of attention by the concurrent task reduced the contrast sensitivity for gratings with low temporal frequencies much more profoundly than for gratings with high temporal frequencies and for flashed gratings. The analysis revealed that the temporal contrast sensitivity function had a more band-pass shape with poor attention. Additional experiments showed that this was also true when the target was presented in various levels of luminance noise. These results suggest that regardless of the presence of external noise, attention extensively modulates visual sensitivity for sustained retinal inputs.

Refractive surgery in anisometropic adult patients induce plastic changes in primary visual cortex

To prospectively study the effect of refractive surgery in the primary visual cortex of adult anisometropic and isometropic myopic patients. Two anisometropic and two isometropic myopic patients were examined with multifocal functional magnetic resonance imaging technique (mffMRI) before refractive surgery and at 3, 6, 9 and 12 months postoperatively. Two controls without refractive surgery were also examined with mffMRI in the beginning and in the end of the study. Anisometropic patients had only their more myopic eye operated to correct the anisometropia. The myopic isometropic patients had their both eyes operated. Operated anisometropic eyes showed 65% reduced amount of active voxels in foveal data at 12 months postoperatively compared with the preoperative situation. In unoperated anisometropic eyes, the corresponding value was 86% and in myopic patients and controls 31% and 1%, respectively. To confirm this finding, the number of activated voxels representing the innermost ring of the stimulus was also calculated, and an exactly similar phenomenon was encountered in the anisometropic patients. Both anisometropic patients improved the best-spectacle-corrected visual acuity in the operated eye after refractive surgery. Our results suggest that plastic changes may take place in the primary visual cortex of anisometropic adult patients after refractive surgery.

Visual Crowding Is Correlated with Awareness

Crowding by nearby features causes identification failures in the peripheral visual field. However, prominent visual features can sometimes fail to reach awareness, causing scenes to be incorrectly interpreted. Here we examine whether awareness of the flanking features is necessary for crowding to occur. Flankers that were physically present were rendered perceptually absent with adaptation-induced blindness. In a letter identification task, targets were presented unflanked or with up to four flanker letters. On each trial, observers reported both the number of letters they perceived and the identity of a target letter. This paradigm allowed trial-by-trial assessment of awareness and crowding and ensured that both targets and flankers were attended. Target-letter identification performance was correlated with the number of flanking letters that were perceived on a given trial, regardless of the number that were physically present. Our data demonstrate that crowding can be released when flanking elements at attended locations are suppressed from visual awareness.