Changes in pupil diameter entrained by cortically initiated changes in attention

Functional benefits of cognitively driven pupil-size changes

Pupil-size changes are typically associated with the pupil light response (PLR), where they are driven by the physical entry of light into the eye. However, pupil-size changes are also influenced by various cognitive processes, where they are driven by higher-level cognition. For example, the strength of the PLR is not solely affected by physical properties of the light but also by cognitive factors, such as whether the source of light is attended or not, which results in an increase or decrease in the strength of the PLR. Surprisingly, although cognitively driven pupil-size changes have been the focus of extensive research, their possible functions are rarely discussed. Here we consider the relative (dis)advantages of small versus large pupils in different situations from a theoretical point of view, and compare these to empirical results showing how pupil size actually changes in these situations. Based on this, we suggest that cognitively driven pupil-size changes optimize vision either through preparation, embodied representations, or a differential emphasis on central or peripheral vision. More generally, we argue that cognitively driven pupil-size changes are a form of sensory tuning: a subtle adjustment of the eyes to optimize vision for the current situation and the immediate future. This article is categorized under: Neuroscience > Cognition Neuroscience > Physiology Neuroscience > Behavior.

Changes in attentional breadth scale with the demands of Kanizsa-figure object completion-evidence from pupillometry

The present study investigated whether the integration of separate parts into a whole-object representation varies with the amount of available attentional resources. To this end, two experiments were performed, which required observers to maintain central fixation while searching in peripheral vision for a target among various distractor configurations. The target could either be a "grouped" whole-object Kanizsa figure, or an "ungrouped" configuration of identical figural parts, but which do not support object completion processes to the same extent. In the experiments, accuracies and changes in pupil size were assessed, with the latter reflecting a marker of the covert allocation of attention in the periphery. Experiment 1 revealed a performance benefit for grouped (relative to ungrouped) targets, which increased with decreasing distance from fixation. By contrast, search for ungrouped targets was comparably poor in accuracy without revealing any eccentricity-dependent variation. Moreover, measures of pupillary dilation mirrored this eccentricity-dependent advantage in localizing grouped targets. Next, in Experiment 2, an additional attention-demanding foveal task was introduced in order to further reduce the availability of attentional resources for the peripheral detection task. This additional task hampered performance overall, alongside with corresponding pupil size changes. However, there was still a substantial benefit for grouped over ungrouped targets in both the behavioral and the pupillometric data. This shows that perceptual grouping scales with the allocation of attention even when only residual attentional resources are available to trigger the representation of a complete (target) object, thus illustrating that object completion operates in the "near absence" of attention.

Broadening of attention dilates the pupil

Inconclusive evidence suggests that the pupil is more dilated when the breadth of attention is broad compared to narrow. To further investigate this relationship, we recorded pupil size from healthy volunteers while inducing trial-wise changes in breadth of attention using a shape-discrimination task where participants had to remember the location of a gap in a small or a large circle. A visual search task with targets presented at different distances from the centre of the screen was used to behaviourally assess the success of the manipulation of breadth of attention. Data were analysed using a generalised additive mixed model to test the experimental effects on pupil size after controlling for the effects of gaze location and eye vergence. The results showed that the pupil was more dilated in the broad-breadth-of-attention condition compared to the narrow-breadth-of-attention condition. However, the effect of attentional breadth on visual search performance was not mediated by pupil size, suggesting that more research is needed to understand the functional role of pupil dilation in relation to breadth of attention.

Emphasis on peripheral vision is accompanied by pupil dilation

People are best able to detect stimuli in peripheral vision when their pupils are large, and best able to discriminate stimuli in central vision when their pupils are small. However, it is unclear whether our visual system makes use of this by dilating the pupils when attention is directed towards peripheral vision. Therefore, throughout three experiments (N = 100), we tested whether pupil size adapts to the "breadth" of attention. We found that pupils dilate with increasing attentional breadth, both when attention is diffusely spread and when attention is directed at specific locations in peripheral vision. Based on our results and others, we propose that cognitively driven pupil dilation is not an epiphenomenal marker of locus coeruleus activity, as is often assumed, but rather is an adaptive response that reflects an emphasis on peripheral vision.

Methods in cognitive pupillometry: Design, preprocessing, and statistical analysis

Cognitive pupillometry is the measurement of pupil size to investigate cognitive processes such as attention, mental effort, working memory, and many others. Currently, there is no commonly agreed-upon methodology for conducting cognitive-pupillometry experiments, and approaches vary widely between research groups and even between different experiments from the same group. This lack of consensus makes it difficult to know which factors to consider when conducting a cognitive-pupillometry experiment. Here we provide a comprehensive, hands-on guide to methods in cognitive pupillometry, with a focus on trial-based experiments in which the measure of interest is the task-evoked pupil response to a stimulus. We cover all methodological aspects of cognitive pupillometry: experimental design, preprocessing of pupil-size data, and statistical techniques to deal with multiple comparisons when testing pupil-size data. In addition, we provide code and toolboxes (in Python) for preprocessing and statistical analysis, and we illustrate all aspects of the proposed workflow through an example experiment and example scripts.

Influence of the Location of a Decision Cue on the Dynamics of Pupillary Light Response

The pupils of the eyes reflexively constrict in light and dilate in dark to optimize retinal illumination. Non-visual cognitive factors, like attention, arousal, decision-making, etc., also influence pupillary light response (PLR). During passive viewing, the eccentricity of a stimulus modulates the pupillary aperture size driven by spatially weighted corneal flux density (CFD), which is the product of luminance and the area of the stimulus. Whether the scope of attention also influences PLR remains unclear. In this study, we contrasted the pupil dynamics between diffused and focused attentional conditions during decision-making, while the global CFD remained the same in the two conditions. A population of 20 healthy humans participated in a pair of forced choice tasks. They distributed attention to the peripheral decision cue in one task, and concentrated at the center in the other to select the target from four alternatives for gaze orientation. The location of this cue did not influence participants' reaction time (RT). However, the magnitude of constriction was significantly less in the task that warranted attention to be deployed at the center than on the periphery. We observed similar pupil dynamics when participants either elicited or canceled a saccadic eye movement, which ruled out pre-saccadic obligatory attentional orientation contributing to PLR. We further addressed how the location of attentional deployment might have influenced PLR. We simulated a biomechanical model of PLR with visual stimulation of different strengths as inputs corresponding to the two attentional conditions. In this homeomorphic model, the computational characteristic of each element was derived from the physiological and/or mechanical properties of the corresponding biological element. The simulation of this model successfully mimicked the observed data. In contrast to common belief that the global ambient luminosity drives pupillary response, the results of our study suggest that the effective CFD (eCFD) determined via the luminance multiplied by the size of the stimulus at the location of deployed attention in the visual space is critical for the magnitude of pupillary constriction.

Individual pupil size changes as a robust indicator of cognitive familiarity differences

Cognitive psychology has a long history of using physiological measures, such as pupillometry. However, their susceptibility to confounds introduced by stimulus properties, such as color and luminance, has limited their application. Pupil size measurements, in particular, require sophisticated experimental designs to dissociate relatively small changes in pupil diameter due to cognitive responses from larger ones elicited by changes in stimulus properties or the experimental environment. Here, building on previous research, we present a pupillometry paradigm that adapts the pupil to stimulus properties during the baseline period without revealing stimulus meaning or context by using a pixel-scrambled image mask around an intact image. We demonstrate its robustness in the context of pupillary responses to branded product familiarity. Results show larger average and peak pupil dilation for passively viewed familiar product images and an extended later temporal component representing differences in familiarity across participants (starting around 1400 ms post-stimulus onset). These amplitude differences are present for almost all participants at the single-participant level, and vary somewhat by product category. However, amplitude differences were absent during the baseline period. These findings demonstrate that involuntary pupil size measurements combined with the presented paradigm are successful in dissociating cognitive effects of familiarity from physical stimulus confounds.

The confounding effects of eye blinking on pupillometry, and their remedy

Pupillometry, thanks to its strong relationship with cognitive factors and recent advancements in measuring techniques, has become popular among cognitive or neural scientists as a tool for studying the physiological processes involved in mental or neural processes. Despite this growing popularity of pupillometry, the methodological understanding of pupillometry is limited, especially regarding potential factors that may threaten pupillary measurements' validity. Eye blinking can be a factor because it frequently occurs in a manner dependent on many cognitive components and induces a pulse-like pupillary change consisting of constriction and dilation with substantive magnitude and length. We set out to characterize the basic properties of this "blink-locked pupillary response (BPR)," including the shape and magnitude of BPR and their variability across subjects and blinks, as the first step of studying the confounding nature of eye blinking. Then, we demonstrated how the dependency of eye blinking on cognitive factors could confound, via BPR, the pupillary responses that are supposed to reflect the cognitive states of interest. By building a statistical model of how the confounding effects of eye blinking occur, we proposed a probabilistic-inference algorithm of de-confounding raw pupillary measurements and showed that the proposed algorithm selectively removed BPR and enhanced the statistical power of pupillometry experiments. Our findings call for attention to the presence and confounding nature of BPR in pupillometry. The algorithm we developed here can be used as an effective remedy for the confounding effects of BPR on pupillometry.

Visual Strategies Underpinning the Spatiotemporal Demands During Visuomotor Tasks in Predicting Ball Direction

We investigated gaze behavior of expert goalkeepers during the prediction of penalty kicks in different spatiotemporal constraints: penalties taken from 11 and 6 m. From 11 m, goalkeepers were more successful in predicting ball direction, with longer movement time initiation and a visual strategy with more fixations and greater saccade rates than penalties from 6 m, where they exhibited fewer fixations with higher microsaccade rates. As long as the opponent's distance is large and time pressure low, gaze can be frequently shifted between the kicker's body and the ball, due to the low cost of saccades. Conversely, when the objects are close, there is increased reliance on foveal and parafoveal information. In conclusion, when the spatiotemporal constraint is less severe, goalkeepers adopt a visual strategy with more fixations and small saccades. When the spatiotemporal constraint is more severe, they rely on peripheral vision to monitor kickers' movements through the use of microsaccades.

Visuospatial Attention Allocation as an Indicator of Cognitive Deficit in Traumatic Brain Injury: A Systematic Review and Meta-Analysis

Traumatic Brain Injury (TBI) is defined by changes in brain function resulting from external forces acting on the brain and is typically characterized by a host of physiological and functional changes such as cognitive deficits including attention problems. In the present study, we focused on the effect of TBI on the ability to allocate attention in vision (i.e., the use of endogenous and exogenous visual cues) by systematically reviewing previous literature on the topic. We conducted quantitative synthesis of 16 selected studies of visual attention following TBI, calculating 80 effect size estimates. The combined effect size was large (g = 0.79, p < 0.0001) with medium heterogeneity (I² = 68.39%). Subgroup analyses revealed an increase in deficit with moderate-to-severe and severe TBI as compared to mild TBI [F_{(2, 76)} = 24.14, p < 0.0001]. Task type was another key source of variability and subgroup analyses indicated that higher order attention processes were severely affected by TBI [F_{(2, 77)} = 5.66, p = 0.0051). Meta-regression analyses revealed significant improvement in visual attention deficit with time [p(mild) = 0.031, p(moderate-to-severe) = 0.002, p(severe) < 0.0001]. Taken together, these results demonstrate that visual attention is affected by TBI and that regular assessment of visual attention, using a systematic attention allocation task, may provide a useful clinical measure of cognitive impairment and change after TBI.

Pupillary dilation elicited by attending to two disks with different luminance

Pupils become smaller when people attend to a bright disk as compared to a dark disk. However, people can divide their attention into several distinct positions, which is referred to as divided attention, and pupillary responses under such conditions have not been investigated. In this study, we examined how pupils would respond when people attended to two disks presented at two distinct positions by conducting three experiments. We found that the pupillary response when attending to two disks with different luminance was larger than when attending to a single brighter disk and was comparable to that when attending to a single darker disk, whereas the pupillary response when attending to two disks with identical luminance was not larger than when attending to a single disk (irrespective of the disk luminance). Furthermore, we found that the magnitude of pupillary dilation was determined by the magnitude of the luminance difference between two disks. These results make a useful contribution to the literature on human pupillary responses.

Capturing attention improves accommodation: An experimental study in children with ADHD using multiple object tracking

The present study was aimed at assessing the impact of manipulating the attentional load using a multiple object tracking (MOT) task on the dynamics of the accommodative response in children with attention deficit hyperactivity disorder (ADHD). The pupil size was recorded to assess the effectiveness of the experimental manipulation, and the role of ADHD medication was also explored. The accommodative and pupil dynamics (magnitude and variability) were monitored with an open-field autorefractometer (WAM-5500) in 41 children with ADHD (24 non-medicated and 17 medicated) and 21 non-ADHD controls, while they performed the MOT task with four different levels of complexity (i.e., tracking zero, one, two, or three targets). We found that increasing the attentional load caused a heightened accommodative response, showing a negative association between MOT complexity and accommodative lag in children with ADHD and non-ADHD controls. Complementarily, the pupil size increased as a function of task complexity, confirming a successful experimental manipulation. The stability of accommodation was insensitive to the attentional manipulation, but it differed between groups. Specifically, non-medicated children with ADHD exhibited a greater variability of accommodation in comparison to controls. Increasing the attentional load is associated with a reduction in the accommodative lag in children with ADHD and controls. Our findings show that the allocation of attention plays an important role in the dynamics of the accommodative response, which may be of relevance in the diagnosis and treatment of accommodative deficits in children with and without ADHD.

Cultural Differences in Face Recognition and Potential Underlying Mechanisms

The ability to recognize a face is crucial for the success of social interactions. Understanding the visual processes underlying this ability has been the focus of a long tradition of research. Recent advances in the field have revealed that individuals having different cultural backgrounds differ in the type of visual information they use for face processing. However, the mechanisms that underpin these differences remain unknown. Here, we revisit recent findings highlighting group differences in face processing. Then, we integrate these results in a model of visual categorization developed in the field of psychophysics: the RAP framework. On the basis of this framework, we discuss potential mechanisms, whether face-specific or not, that may underlie cross-cultural differences in face perception.

Pupil Diameter Tracks Statistical Structure in the Environment to Increase Visual Sensitivity

Pupil diameter determines how much light hits the retina and, thus, how much information is available for visual processing. This is regulated by a brainstem reflex pathway. Here, we investigate whether this pathway is under the control of internal models about the environment. This would allow adjusting pupil dynamics to environmental statistics to augment information transmission. We present image sequences containing internal temporal structure to humans of either sex and male macaque monkeys. We then measure whether the pupil tracks this temporal structure not only at the rate of luminance variations, but also at the rate of statistics not available from luminance information alone. We find entrainment to environmental statistics in both species. This entrainment directly affects visual processing by increasing sensitivity at the environmentally relevant temporal frequency. Thus, pupil dynamics are matched to the temporal structure of the environment to optimize perception, in line with an active sensing account.SIGNIFICANCE STATEMENT When light hits the retina, the pupil reflexively constricts. This determines how much light and thus how much information is available for visual processing. We show that the rate at which the pupil constricts and dilates is matched to the temporal structure of our visual environment, although this information is not directly contained in the light variations that usually trigger reflexive pupil constrictions. Adjusting pupil diameter in accordance with environmental regularities optimizes information transmission at ecologically relevant temporal frequencies. We show that this is the case in humans and macaque monkeys, suggesting that the reflex pathways that regulate pupil diameter are under some degree of cognitive control across primate species.

Tuning the Senses: How the Pupil Shapes Vision at the Earliest Stage

The pupil responds reflexively to changes in brightness and focal distance to maintain the smallest pupil (and thus the highest visual acuity) that still allows sufficient light to reach the retina. The pupil also responds to a wide variety of cognitive processes, but the functions of these cognitive responses are still poorly understood. In this review, I propose that cognitive pupil responses, like their reflexive counterparts, serve to optimize vision. Specifically, an emphasis on central vision over peripheral vision results in pupil constriction, and this likely reflects the fact that central vision benefits most from the increased visual acuity provided by small pupils. Furthermore, an intention to act with a bright stimulus results in preparatory pupil constriction, which allows the pupil to respond quickly when that bright stimulus is subsequently brought into view. More generally, cognitively driven pupil responses are likely a form of sensory tuning: a subtle adjustment of the eyes to optimize their properties for the current situation and the immediate future. Expected final online publication date for the Annual Review of Vision Science, Volume 6 is September 15, 2020. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Effects of stimulus size, eccentricity, luminance, and attention on pupillary light response examined by concentric stimulus

Previous studies show that the amplitude of pupillary light response (PLR) depends on the corneal flux density (CFD), which is the product of stimulus area by luminance. However, the contribution of CFD has been investigated only when the stimulus was centered on the fovea, whereas perceived luminance to pupillary response would reduce with stimulus eccentricity. Additionally, it has been shown recently that attentional state modulates pupillary response. In this study, we aimed to clarify the complete mechanisms of PLR by manipulating the stimulus size, eccentricity, luminance, and the participants' attentional states. We focused on four indices to examine PLR, that is, pupillary latency (PL), maximum constriction velocity (MCV), maximum constriction (MC), and mean pupil change (MPC). Results showed that PL was a function of CFD, whereas MCV, MC, and MPC were functions of both CFD and stimulus eccentricity. Furthermore, the magnitude of effect due to stimulus eccentricity for MCV and MC was different from that for MPC. These results provided new evidence that the different processing systems in PLR existed.

The effect of pupil size and peripheral brightness on detection and discrimination performance

It is easier to read dark text on a bright background (positive polarity) than to read bright text on a dark background (negative polarity). This positive-polarity advantage is often linked to pupil size: A bright background induces small pupils, which in turn increases visual acuity. Here we report that pupil size, when manipulated through peripheral brightness, has qualitatively different effects on discrimination of fine stimuli in central vision and detection of faint stimuli in peripheral vision. Small pupils are associated with improved discrimination performance, consistent with the positive-polarity advantage, but only for very small stimuli that are at the threshold of visual acuity. In contrast, large pupils are associated with improved detection performance. These results are likely due to two pupil-size related factors: Small pupils increase visual acuity, which improves discrimination of fine stimuli; and large pupils increase light influx, which improves detection of faint stimuli. Light scatter is likely also a contributing factor: When a display is bright, light scatter creates a diffuse veil of retinal illumination that reduces perceived image contrast, thus impairing detection performance. We further found that pupil size was larger during the detection task than during the discrimination task, even though both tasks were equally difficult and similar in visual input; this suggests that the pupil may automatically assume an optimal size for the current task. Our results may explain why pupils dilate in response to arousal: This may reflect an increased emphasis on detection of unpredictable danger, which is crucially important in many situations that are characterized by high levels of arousal. Finally, we discuss the implications of our results for the ergonomics of display design.

IR-camera-based measurements of 2D/3D cognitive fatigue in 2D/3D display system using task-evoked pupillary response

This study was carried out to evaluate a method used to measure three-dimensional (3D) cognitive fatigue based on the pupillary response. This technique was designed to overcome measurement burdens by using non-contact methods. The pupillary response is related to cognitive function by a neural pathway and may be an indicator of 3D cognitive fatigue. Twenty-six undergraduate students (including 14 women) watched both 2D and 3D versions of a video for 70 min. The participants experienced visual fatigue after viewing the 3D content. Measures such as subjective rating, response time, event-related potential latency, heartbeat-evoked potential (HEP) alpha power, and task-evoked pupillary response (TEPR) latency were significantly different. Multitrait-multimethod matrix analysis indicated that HEP and TEPR latency measures had stronger reliability and higher correlations with 3D cognitive fatigue than other measures. TEPR latency may be useful for quantitatively determining 3D visual fatigue, as it can be easily used to evaluate 3D visual fatigue using a non-contact method without measuring burden.

Brief Report: Visual Perception, Task-Induced Pupil Response Trajectories and ASD Features in Children

We applied a trajectory-based analysis to eye tracking data in order to quantify individualized patterns of pupil response in the context of global-local processing that may be associated with autism spectrum disorder (ASD) features. Multiple pupil response trajectories across both global and local conditions were identified. Using the combined trajectory patterns for global and local conditions for each individual, we were able to identify three groups based on trajectory group membership that were thought to reflect perceptual strategy. Results indicated that the proportion of children with ASD was significantly greater in the group demonstrating a local-focus response. This research presents a novel analytic approach to the objective characterization of individualized pupil response patterns that are associated with ASD features.

Tracking working memory maintenance with pupillometry

Phasic pupillary responses were used to track the active maintenance of information in working memory (WM). In seven experiments participants performed various change detection tasks while their pupils were continuously recorded. Across the experiments phasic pupillary responses increased as the number of maintained items increased up to around 4-5 items consistent with behavioral estimates of capacity. Combining data across experiments demonstrated that phasic pupillary responses were related to behavioral estimates of capacity. Furthermore, phasic pupillary responses demonstrated WM load-dependent relations only when active maintenance was required. When instructed to passively stare at the items or to drop items from WM, the pupil remained near baseline levels. These phasic pupillary responses also tracked the time course of maintenance demonstrating sustained responses early in the delay period, but declined thereafter. Finally, phasic pupillary responses tracked selection processes at encoding (filtering and pre-cues), but did not suggest evidence for item removal following retro-cues. These results are consistent with the notion that maintaining items in WM requires the allocation of effortful attention and further suggest that phasic pupillary responses can be used to track the active maintenance of items in WM.

Task-induced pupil response and visual perception in adults

We assessed whether there are differences in pupil response that underlie the selection of local vs. global parts of a stimulus array in healthy adults. We designed a Navon Figures eyetracking paradigm (i.e. large figure composed of small figures), requiring an individual to vary only the information attended to within an image. We found that participants have a characteristic constriction of the pupil waveform during selection of local information relative to global information. Because stimuli and lighting conditions were identical across conditions, this indicates that pupil changes may serve in a visual filtering mechanism important for attentional selection. This work represents the first characterization of pupil response in the context of selective attention, suggesting that mechanisms underlying the earliest stages of visual processes could be relevant for perception and visual selection.

A linear oscillator model predicts dynamic temporal attention and pupillary entrainment to rhythmic patterns

Rhythm is a ubiquitous feature of music that induces specific neural modes of processing. In this paper, we assess the potential of a stimulus-driven linear oscillator model (57) to predict dynamic attention to complex musical rhythms on an instant-by-instant basis. We use perceptual thresholds and pupillometry as attentional indices against which to test our model predictions. During a deviance detection task, participants listened to continuously looping, multiinstrument, rhythmic patterns, while being eye-tracked. Their task was to respond anytime they heard an increase in intensity (dB SPL). An adaptive thresholding algorithm adjusted deviant intensity at multiple probed temporal locations throughout each rhythmic stimulus. The oscillator model predicted participants’ perceptual thresholds for detecting deviants at probed locations, with a low temporal salience prediction corresponding to a high perceptual threshold and vice versa. A pupil dilation response was observed for all deviants. Notably, the pupil dilated even when participants did not report hearing a deviant. Maximum pupil size and resonator model output were significant predictors of whether a deviant was detected or missed on any given trial. Besides the evoked pupillary response to deviants, we also assessed the continuous pupillary signal to the rhythmic patterns. The pupil exhibited entrainment at prominent periodicities present in the stimuli and followed each of the different rhythmic patterns in a unique way. Overall, these results replicate previous studies using the linear oscillator model to predict dynamic attention to complex auditory scenes and extend the utility of the model to the prediction of neurophysiological signals, in this case the pupillary time course; however, we note that the amplitude envelope of the acoustic patterns may serve as a similarly useful predictor. To our knowledge, this is the first paper to show entrainment of pupil dynamics by demonstrating a phase relationship between musical stimuli and the pupillary signal.

Are Fast Complex Movements Unimaginable? Pupillometric Studies of Motor Imagery in Expert Piano Playing

Motor imagery (MI; mental simulation of actions) shares certain mental representations and processes with executed movement (ME). This neurocognitive overlap between MI and ME may explain why the systematic use of MI improves skilled performance in numerous domains. Unfortunately, the attentional mechanisms underlying MI remain unresolved. Therefore, the present studies investigated the role of attentional effort (as measured by pupil dilation) in MI. We evaluated the effects of movement complexity and speed on expert pianists' pupil dilation as they physically executed and used MI to perform easy/complex and slow/fast music phrases. Results revealed that easy movements required similar levels of attentional effort during MI and ME. However, during complex movements performed at a fast speed, the correspondence between execution and imagery of movement was disrupted.

Top-down, contextual entrainment of neuronal oscillations in the auditory thalamocortical circuit

Our results indicate that nonhuman primates detect complex repeating acoustic sequences in a continuous auditory stream, which is an important precursor for human speech learning and perception. We demonstrate that oscillatory entrainment, known to support the attentive perception of rhythmic stimulus sequences, can occur for rhythms defined solely by stimulus context rather than physical boundaries. As opposed to acoustically driven entrainment by rhythmic tone sequences demonstrated previously, this form of entrainment relies on the brain’s ability to group auditory inputs based on their statistical regularities. The internally initiated, context-driven modulation of excitability in the medial pulvinar prior to A1 supports the notion of top-down entrainment.

Prior studies have shown that repetitive presentation of acoustic stimuli results in an alignment of ongoing neuronal oscillations to the sequence rhythm via oscillatory entrainment by external cues. Our study aimed to explore the neural correlates of the perceptual parsing and grouping of complex repeating auditory patterns that occur based solely on statistical regularities, or context. Human psychophysical studies suggest that the recognition of novel auditory patterns amid a continuous auditory stimulus sequence occurs automatically halfway through the first repetition. We hypothesized that once repeating patterns were detected by the brain, internal rhythms would become entrained, demarcating the temporal structure of these repetitions despite lacking external cues defining pattern on- or offsets. To examine the neural correlates of pattern perception, neuroelectric activity of primary auditory cortex (A1) and thalamic nuclei was recorded while nonhuman primates passively listened to streams of rapidly presented pure tones and bandpass noise bursts. At arbitrary intervals, random acoustic patterns composed of 11 stimuli were repeated five times without any perturbance of the constant stimulus flow. We found significant delta entrainment by these patterns in the A1, medial geniculate body, and medial pulvinar. In A1 and pulvinar, we observed a statistically significant, pattern structure-aligned modulation of neuronal firing that occurred earliest in the pulvinar, supporting the idea that grouping and detecting complex auditory patterns is a top-down, context-driven process. Besides electrophysiological measures, a pattern-related modulation of pupil diameter verified that, like humans, nonhuman primates consciously detect complex repetitive patterns that lack physical boundaries.

Grounding by Attention Simulation in Peripersonal Space: Pupils Dilate to Pinch Grip But Not Big Size Nominal Classifier

Grammatical categories represent implicit knowledge, and it is not known if such abstract linguistic knowledge can be continuously grounded in real-life experiences, nor is it known what types of mental states can be simulated. A former study showed that attention bias in peripersonal space (PPS) affects reaction times in grammatical congruency judgments of nominal classifiers, suggesting that simulated semantics may include reenactment of attention. In this study, we contrasted a Chinese nominal classifier used with nouns denoting pinch grip objects with a classifier for nouns with big object referents in a pupil dilation experiment. Twenty Chinese native speakers read grammatical and ungrammatical classifier-noun combinations and made grammaticality judgment while their pupillary responses were measured. It was found that their pupils dilated significantly more to the pinch grip classifier than to the big object classifier, indicating attention simulation in PPS. Pupil dilations were also significantly larger with congruent trials on the whole than in incongruent trials, but crucially, congruency and classifier semantics were independent of each other. No such effects were found in controls.

ADHD subjects fail to suppress eye blinks and microsaccades while anticipating visual stimuli but recover with medication

Oculomotor behavior and parameters are known to be affected by the allocation of attention and could potentially be used to investigate attention disorders. We explored the oculomotor markers of Attention-deficit/hyperactivity disorder (ADHD) that are involuntary and quantitative and that could be used to reveal the core-affected mechanisms, as well as be used for differential diagnosis. We recorded eye movements in a group of 22 ADHD-diagnosed patients with and without medication (methylphenidate) and in 22 control observers while performing the test of variables of attention (t.o.v.a.). We found that the average microsaccade and blink rates were higher in the ADHD group, especially in the time interval around stimulus onset. These rates increased monotonically over session time for both groups, but with significantly faster increments in the unmedicated ADHD group. With medication, the level and time course of the microsaccade rate were fully normalized to the control level, regardless of the time interval within trials. In contrast, the pupil diameter decreased over time within sessions and significantly increased above the control level with medication. We interpreted the suppression of microsaccades and eye blinks around the stimulus onset as reflecting a temporal anticipation mechanism for the transient allocation of attention, and their overall rates as inversely reflecting the level of arousal. We suggest that ADHD subjects fail to maintain sufficient levels of arousal during a simple and prolonged task, which limits their ability to dynamically allocate attention while anticipating visual stimuli. This impairment normalizes with medication and its oculomotor quantification could potentially be used for differential diagnosis.

The reinforcing and subjective effects of intravenous and intranasal buprenorphine in heroin users

Abuse of buprenorphine (BUP) by the intravenous (IV) route has been documented in several studies, and reports of intranasal (IN) abuse are increasing. However, no studies have directly compared the effects of BUP when it is administered intranasally and intravenously. The present secondary analysis used data from two separate studies to compare the reinforcing and subjective effects of IV and IN buprenorphine. One study evaluated IV buprenorphine (N=13) and the other evaluated IN buprenorphine (N=12). Participants were maintained on 2 mg sublingual (SL) BUP and tested with each intranasal or intravenous buprenorphine test dose (0 mg, 2 mg, 4 mg, 8 mg, and 16 mg). During morning laboratory sessions, participants received money (US $20) and sample doses of IN or IV BUP, and then completed subjective effects questionnaires. Later that day, they completed a self-administration task to receive 10% portions of the drug and/or money they previously sampled. In general, positive subjective ratings for both IV and IN BUP were significantly greater than placebo, with IV BUP having a greater effect than IN BUP. All active BUP doses (IV and IN) maintained significantly higher progressive ratio breakpoint values than placebo, but breakpoint values for IV BUP were greater than for IN BUP. Buprenorphine is an effective maintenance treatment for opioid dependence, valued for its ability to reduce the positive subjective effects of other opioids. Nevertheless, the present data demonstrate that in participants maintained on a low dose of SL BUP, the medication itself has abuse liability when used intravenously or intranasally.

Tracking the allocation of attention using human pupillary oscillations

The muscles that control the pupil are richly innervated by the autonomic nervous system. While there are central pathways that drive pupil dilations in relation to arousal, there is no anatomical evidence that cortical centers involved with visual selective attention innervate the pupil. In this study, we show that such connections must exist. Specifically, we demonstrate a novel Pupil Frequency Tagging (PFT) method, where oscillatory changes in stimulus brightness over time are mirrored by pupil constrictions and dilations. We find that the luminance–induced pupil oscillations are enhanced when covert attention is directed to the flicker stimulus and when targets are correctly detected in an attentional tracking task. These results suggest that the amplitudes of pupil responses closely follow the allocation of focal visual attention and the encoding of stimuli. PFT provides a new opportunity to study top–down visual attention itself as well as identifying the pathways and mechanisms that support this unexpected phenomenon.

Processing speed training increases the efficiency of attentional resource allocation in young adults

Cognitive training has been shown to improve performance on a range of tasks. However, the mechanisms underlying these improvements are still unclear. Given the wide range of transfer effects, it is likely that these effects are due to a factor common to a wide range of tasks. One such factor is a participant's efficiency in allocating limited cognitive resources. The impact of a cognitive training program, Processing Speed Training (PST), on the allocation of resources to a set of visual tasks was measured using pupillometry in 10 young adults as compared to a control group of a 10 young adults (n = 20). PST is a well-studied computerized training program that involves identifying simultaneously presented central and peripheral stimuli. As training progresses, the task becomes increasingly more difficult, by including peripheral distracting stimuli and decreasing the duration of stimulus presentation. Analysis of baseline data confirmed that pupil diameter reflected cognitive effort. After training, participants randomized to PST used fewer attentional resources to perform complex visual tasks as compared to the control group. These pupil diameter data indicated that PST appears to increase the efficiency of attentional resource allocation. Increases in cognitive efficiency have been hypothesized to underlie improvements following experience with action video games, and improved cognitive efficiency has been hypothesized to underlie the benefits of PST in older adults. These data reveal that these training schemes may share a common underlying mechanism of increasing cognitive efficiency in younger adults.

Neuro-ophthalmology Annual Review

PURPOSE

To provide a clinical update of the neuro-ophthalmology literature over the last twelve months.

DESIGN

This is an annual review of current literature from August 1, 2011 to August 1, 2012.

METHODS

The authors conducted a one year English language neuro-ophthalmology literature search using PubMed from August 1, 2011 to August 1, 2012 using the following search terms: pupil abnormalities, eye movements, diseases of muscle and musculoskeletal junction, optic nerve disorders, optic neuritis and multiple sclerosis, chiasm and posterior primary visual pathway lesions, increased intracranial pressure and related entities, tumors (e.g., meningioma) and aneurysm affecting the visual pathways, vascular diseases, higher visual functions, advances in neuroimaging, and miscellaneous topics in neuro-ophthalmology. The authors included original articles, review articles, and case reports, which revealed the new aspects and updates in neuro-ophthalmology. Letters to the editor, unpublished work, and abstracts were not included in this annual literature review. We propose to update the practicing clinical ophthalmologist on the most clinically relevant literature from the past year. However, this review is not meant to be all-inclusive and highlights only the literature most applicable to the practicing clinical ophthalmologist.

RESULTS

We reviewed the literature over the past year in neuro-ophthalmology of potential interest and relevance to the comprehensive ophthalmologist.

CONCLUSION

This annual review provides a brief update on a number of neuroophthalmic conditions that might be of interest to the practicing clinical ophthalmologist.