Rapid Stimulus Presentation Research Articles

A Recurrent Temporal Model for Semantic Levels Categorization Based on Human Visual System.

Humans can categorize an object in different semantic levels. For example, a dog can be categorized as an animal (superordinate), a terrestrial animal (basic), or a dog (subordinate). Recent studies have shown that the duration of stimulus presentation can affect the mechanism of categorization in the brain. Rapid stimulus presentation will not allow top-down influences to be applied on the visual cortex, whereas in the nonrapid, top-down influences can be established and the final result will be different. In this paper, a spiking recurrent temporal model based on the human visual system for semantic levels of categorization is introduced. We showed that the categorization problem for up-right and inverted images can be solved without taking advantage of feedback, but for the occlusion and deletion problems, top-down feedback is necessary. The proposed computational model has three feedback paths that express the effects of expectation and the perceptual task, and it is described by the type of problem that the model seeks to solve and the level of categorization. Depending on the semantic level of the asked question, the model changes its neuronal structure and connections. Another application of recursive paths is solving the expectation effect problem, that is, compensating the reduce in firing rate by the top-down influences due to the available features in the object. In addition, in this paper, a psychophysical experiment is performed and top-down influences are investigated through this experiment. In this experiment, by top-down influences, the speed and accuracy of the categorization of the subjects increased for all three categorization levels. In both the presence and absence of top-down influences, the remarkable point is the superordinate advantage.

Print-specific N170 involves multiple subcomponents for Japanese Hiragana

Print-specific N170 in event-related potentials is generally considered to reflect relatively automatic processing for letter strings, which is crucial for fluent reading. However, our previous studies demonstrated that print-specific N170 for transparent Japanese Hiragana script consists of at least two subcomponents under rapid stimulus presentation: an attention-related left-lateralized N170 and a bilateral N170 associated with more automatic orthographic processes (Okumura, Kasai & Murohashi, 2014, 2015). The present study aimed to confirm the latter component by controlling presentation frequency of letters and nonlinguistic visual controls (i.e., symbols), but found a quite different pattern of results; an enhanced occipito-temporal positivity for words (80–120ms poststimulus) followed by the typical left-lateralized N170 and an enhanced parietal negativity for nonwords (150–200ms). These results should provide further insights into the interaction processes between attention and early stages of print processing.

The Effects of Rate on Single-Word Reading Assessment

The purpose of this study was to examine the effects of introducing rapid stimulus presentation durations while limiting response durations on the decoding profiles of college students with reading disorders. Eighteen college-aged individuals with typical reading abilities and 12 college-aged adults who exhibited reading difficulties participated. Participants completed a series of 4 experimental word-naming tasks. Two Word Attack subtests and 2 Word Identification subtests were administered while introducing more rapid stimulus presentation durations along with limited response times. Standard scores and response times were collected. Each individual's results were subjected to a subtyping procedure based on relative decoding strengths and weaknesses. More rapid conditions were associated with higher sight word decoding scores and lower phonological decoding scores. The results indicated that the subtyping patterns differed drastically depending on the presentation conditions. The authors hypothesize that the experimental conditions potentially yield a more reliable assessment of the 2 independent methods of single-word reading. The ability to subtype or categorize readers on the basis of their relative strengths and weaknesses is highly dependent on the reliability of the measures used to assess those relative strengths and weaknesses.

Using decision models to study the time course of visual recognition

Primates’ ability to recognize objects in natural scenes is remarkable. As exemplified by rapid stimulus presentation paradigms, the visual system is both fast and accurate. Computational models have been proposed that predict the level of performance of human participants and how recognition may be affected by visual properties of images. However, these computational models do not make any predictions about reaction times, and cannot explain the time course of information accumulation in the visual cortex. Here we present an initial attempt to fill this gap using a decision model that allows for analysis of both behavioral responses and decision times within a unified framework. Participants performed an object recognition task in natural scenes using a backward masking paradigm with varying stimulus onset asynchrony (SOA) conditions. We estimated decision-related parameters for the task using a hierarchical drift diffusion model, an extension of the most widely used decision model. We examined how the drift rate, a parameter associated with task difficulty, can be used to explain the results, and show that changes in the drift rate alone does not seem to account for the distribution of reaction times under different masking conditions. Interestingly we find that both the SOA and image properties affect the variance of the drift rate, and that this change does not seem to simply reflect variability in the stimulus properties across conditions. We speculate that it may reflect multiple processing strategies employed by the visual system to process information. Our results suggest that decision models may constitute a promising tool for understanding the brain mechanisms underlying object recognition. Meeting abstract presented at VSS 2012

Women's Greater Ability to Perceive Happy Facial Emotion Automatically: Gender Differences in Affective Priming

There is evidence that women are better in recognizing their own and others' emotions. The female advantage in emotion recognition becomes even more apparent under conditions of rapid stimulus presentation. Affective priming paradigms have been developed to examine empirically whether facial emotion stimuli presented outside of conscious awareness color our impressions. It was observed that masked emotional facial expression has an affect congruent influence on subsequent judgments of neutral stimuli. The aim of the present study was to examine the effect of gender on affective priming based on negative and positive facial expression. In our priming experiment sad, happy, neutral, or no facial expression was briefly presented (for 33 ms) and masked by neutral faces which had to be evaluated. 81 young healthy volunteers (53 women) participated in the study. Subjects had no subjective awareness of emotional primes. Women did not differ from men with regard to age, education, intelligence, trait anxiety, or depressivity. In the whole sample, happy but not sad facial expression elicited valence congruent affective priming. Between-group analyses revealed that women manifested greater affective priming due to happy faces than men. Women seem to have a greater ability to perceive and respond to positive facial emotion at an automatic processing level compared to men. High perceptual sensitivity to minimal social-affective signals may contribute to women's advantage in understanding other persons' emotional states.

Cortical mechanisms of auditory spatial attention in a target detection task

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

It’s About Time

Accurate identification of emotional expressions is important to social interaction. We examined the relations among shyness, sociability, and the accuracy of categorization of facial expression of emotions in a sample of 127 undergraduates. Individual differences in sociability, but not shyness, were significantly related to categorization accuracy under conditions of limited presentation time, but not under circumstances of unlimited stimulus presentation time. Adults self-rated as low to moderate in sociability were significantly less accurate in categorizing facial expressions of emotion, albeit only under conditions of rapid stimulus presentation. These results suggest that individual differences in sociability and social exposure may influence the ability to categorize facial expressions of emotions.

Influence of the interstimulus interval on temporal processing and learning: testing the state-dependent network model

The ability to determine the interval and duration of sensory events is fundamental to most forms of sensory processing, including speech and music perception. Recent experimental data support the notion that different mechanisms underlie temporal processing in the subsecond and suprasecond range. Here, we examine the predictions of one class of subsecond timing models: state-dependent networks. We establish that the interval between the comparison and the test interval, interstimulus interval (ISI), in a two-interval forced-choice discrimination task, alters the accuracy of interval discrimination but not the point of subjective equality-i.e. while timing was impaired, subjective time contraction or expansion was not observed. We also examined whether the deficit in temporal processing produced by short ISIs can be reduced by learning, and determined the generalization patterns. These results show that training subjects on a task using a short or long ISI produces dramatically different generalization patterns, suggesting different forms of perceptual learning are being engaged. Together, our results are consistent with the notion that timing in the range of hundreds of milliseconds is local as opposed to centralized, and that rapid stimulus presentation rates impair temporal discrimination. This interference is, however, decreased if the stimuli are presented to different sensory channels.

Increased Anterior Cingulate Cortical Activity in Response to Fearful Faces: A Neurophysiological Biomarker that Predicts Rapid Antidepressant Response to Ketamine

Most patients with major depressive disorder (MDD) experience a period of lengthy trial and error when trying to find optimal antidepressant treatment; identifying biomarkers that could predict response to antidepressant treatment would be of enormous benefit. We tested the hypothesis that pretreatment anterior cingulate cortex (ACC) activity could be a putative biomarker of rapid antidepressant response to ketamine, in line with previous findings that investigated the effects of conventional antidepressants. We also investigated patterns of ACC activity to rapid presentation of fearful faces compared with the normal habituation observed in healthy subjects. We elicited ACC activity in drug-free patients with MDD (n = 11) and healthy control subjects (n = 11) by rapidly presenting fearful faces, a paradigm known to activate rostral regions of the ACC. Spatial-filtering analyses were performed on magnetoencephalographic (MEG) recordings, which offer the temporal precision necessary to estimate ACC activity elicited by the rapid presentation of stimuli. Magnetoencephalographic recordings were obtained only once for both patients and control subjects. Patients were subsequently administered a single ketamine infusion followed by assessment of depressive symptoms 4 hours later. Although healthy subjects had decreased neuromagnetic activity in the rostral ACC across repeated exposures, patients with MDD showed robust increases in pretreatment ACC activity. Notably, this increase was positively correlated with subsequent rapid antidepressant response to ketamine. Exploratory analyses showed that pretreatment amygdala activity was negatively correlated with change in depressive symptoms. Pretreatment rostral ACC activation may be a useful biomarker that identifies a subgroup of patients who will respond favorably to ketamine's antidepressant effects.

Can subitizing survive the attentional blink? An ERP study

This study was done to test whether subitizing versus counting are attention demanding based on whether they can be performed during the attentional blink (AB). ERPs were recorded while participants performed a task requiring them to judge the number of dots presented and this judgment task either followed the presentation of a task-relevant item in a rapid stimulus presentation stream (dual-task) or the potential target was task irrelevant (single-task). The behavioral data demonstrated that T2 accuracies decreased as a function of the number of dots not only in counting range, but also in subitizing range. The ERP results showed a delayed P3 component in the dual-task condition, and this was equally true for both subitizing and counting conditions. Furthermore, the P3 amplitude was reduced during the AB, and this was still equally true for both the subitizing and counting conditions. The present results suggest that both subitizing and counting require attention, and that subitizing is not a purely pre-attentive process.

Exact Bayesian bin classification: a fast alternative to Bayesian classification and its application to neural response analysis

We investigate the general problem of signal classification and, in particular, that of assigning stimulus labels to neural spike trains recorded from single cortical neurons. Finding efficient ways of classifying neural responses is especially important in experiments involving rapid presentation of stimuli. We introduce a fast, exact alternative to Bayesian classification. Instead of estimating the class-conditional densities p(x|y) (where x is a scalar function of the feature[s], y the class label) and converting them to P(y|x) via Bayes' theorem, this probability is evaluated directly and without the need for approximations. This is achieved by integrating over all possible binnings of x with an upper limit on the number of bins. Computational time is quadratic in both the number of observed data points and the number of bins. The algorithm also allows for the computation of feedback signals, which can be used as input to subsequent stages of inference, e.g. neural network training. Responses of single neurons from high-level visual cortex (area STSa) to rapid sequences of complex visual stimuli are analysed. Information latency and response duration increase nonlinearly with presentation duration, suggesting that neural processing speeds adapt to presentation speeds.

The development of the length of the temporal window of integration for rapidly presented auditory information as indexed by MMN

Objective The length of the temporal window integrating successive auditory stimuli into unitary percepts has been estimated to be less than 200 ms in adults. The aim of the study was to investigate the development of the integrating window in children to determine whether it is similar to young adults. Methods A modified auditory oddball paradigm was presented at a rapid (150–400 ms) onset-to-onset pace during recording of electroencephalogram in two groups of children (aged 5–8 and 9–11 years) and one group of adults. Latencies and amplitudes of the P1, N1, and the mismatch negativity (MMN) components of event-related brain potentials (ERPs) were measured. Results The length of the temporal window of integration (TWI) was shorter in adults (<200 ms) than older children (<300 ms in 9–11-year-olds) and younger children (<350 ms in the 5–8-year-olds). In addition, age-related changes were found in the latency and amplitude of the ERP components. Conclusions The results demonstrate a general maturational development of the auditory evoked potentials and also a specific maturational process for temporal encoding of information in auditory cortex. Significance Rapid stimulus presentation rates can be successfully used in school-aged children to study neural mechanisms of auditory processes.

Abnormal binocular rivalry in unilateral neglect: evidence for a non-spatial mechanism of extinction.

Unilateral spatial neglect (USN) is considered to be an attention deficit, which is primarily related to space. Recent evidence points to the relevance of non-spatially lateralized mechanisms, with impairments found in rapid stimulus presentation conditions. Here we used the phenomenon of binocular rivalry (BR) to explore a non-spatial deficit over long temporal intervals. Six right-hemisphere damaged (RHD) patients with contralesional neglect (USN+), five RHD patients without neglect (USN-) and six normal controls were tested on the basic properties of BR induced by dichoptic presentation of orthogonal gratings at fixation. USN+ patients had much slower perceptual alternations compared to the USN- and normal groups (factors 2.5 and 4, respectively), and were much more sensitive to inter-ocular changes in relative stimulus contrast, which, unlike normals, altered both the suppression and dominance phases. Most notably, a small advantage of one monocular stimulus caused a long-term extinction of the other stimulus in the USN+ group alone. We explain the results in terms of impaired habituation to dominant and attended stimuli, which normally prevents a winner-takes-all behavior and extinction of the weak. This impaired habituation may in turn contribute to inappropriate environmental monitoring and attenuated novelty-seeking behavior.

Repeated fMRI Using Iron Oxide Contrast Agent in Awake, Behaving Macaques at 3 Tesla

Iron oxide contrast agents have been employed extensively in anesthetized rodents to enhance fMRI sensitivity and to study the physiology of cerebral blood volume (CBV) in relation to blood oxygen level-dependent (BOLD) signal following neuronal activation. This study quantified the advantages of exogenous agent for repeated neuroimaging in awake, nonhuman primates using a clinical 3 Tesla scanner. A monocrystalline iron oxide nanoparticle (MION) solution was injected at iron doses of 8 to 10 mg/kg in two macaque monkeys. Adverse behavioral effects due to contrast agent were not observed in either monkey using cumulative doses in excess of 60 mg/kg. Relative to BOLD imaging at 3 Tesla, MION increased functional sensitivity by an average factor of 3 across the brain for a stimulus of long duration. Rapid stimulus presentation attenuated MION signal changes more than BOLD signal changes, due to the slower time constant of the blood volume response relative to BOLD signal. Overall, the contrast agent produced a dramatic improvement in functional brain imaging results in the awake, behaving primate at this field strength.

Effects of Sex, Handedness, Stimulus and Visual Field on “Mental Rotation”

Shepard's mental rotation paradigm (e.g. Shepard and Metzler, 1971) was modified to allow tachistoscopic presentation of stimuli at varying angles of orientation (0° to 180°) in the right and left visual fields. Thirty male and thirty female subjects divided into three handedness groups (right-handers, non-familial and familial left-handers) judged whether a stimulus was a standard form or its mirror image. In general response times for correct judgements (RTc) increased monotonically as a function of angle of orientation though the curves tended to be negatively accelerated rather than linear. Right-handers showed a slower rate of increase in RTc as a function of angle than either left-handed group. Mean RTc and the rate of increase in RTc were equivalent for the two sexes and for the two visual fields. Both mean RTcs and on the rate of increase in RTc varied as a function of the stimulus.Error rates also increased monotonically as a function of angle of orientation. No sex or handedness differences in error rates were found. However, errors increased significantly less rapidly when stimuli were presented in the left visual field. It is argued that right hemisphere specialization for spatial processing minimizes the rate of increase in errors.The present failure to find sex differences may be of interest and it is argued that rapid presentation of stimuli results in subjects setting maximum and minimun response times. Within this relatively restricted “bandwith” of response times males and females may perform spatial tasks equally efficiently. Some confirmation for this hypothesis vs. an alternative based upon differences in hemispheric organization was found in a second experiment.

Serial Learning under Conditions of Rapid Presentation of Stimuli

Serial Learning under Conditions of Rapid Presentation of Stimuli