Psychophysical Tasks Research Articles

Hearing motion in "the mind's ear" - evidence for a vision-to-sound synesthesia

Here we report a previously undescribed vision-to-sound synesthesia. We studied three healthy individuals for whom seeing visual flashes or motion causes the perception of sound (e.g. tapping or buzzing). Consistent with other synesthesias, the visually-induced sound percepts are automatic and cannot be turned off. This synesthesia conferred a distinct advantage on a visual psychophysics task. Synesthetes (n=2) and control (n=8) subjects were presented with rapid rhythmic sequences (similar to Morse code) composed of either auditory beeps or of visual flashes. Subjects judged whether two successive sequences (either both auditory or both visual) were the same or different sequence (2-IFC trials). All subjects performed well on auditory trials (syn: 86% correct, controls: 88%). However, only synesthetes performed well on visual trials with controls performing near 50% chance level (syn: 77%, controls: 57%; difference p[[lt]]0.0005). These results are consistent with synesthetes being able to hear the rhythms on visual trials, with the sound percepts being closely temporally linked to the visual inducers. Next, we measured BOLD fMRI responses to viewing of moving vs. stationary visual dots (a standard MT+ localizer stimulus). Synesthetes (n=3) reported sound percepts for the moving but not the stationary condition and showed enhanced responses to visual motion compared to controls (n=8) on the bilateral superior temporal sulcus (STS), a previously reported audiovisual integration site. The same region was highly responsive to visual stimuli in both synesthete and control subjects, when given a task that encouraged temporally-linked sound imagery. Furthermore, the same STS region responded to purely auditory stimuli in both synesthetes and controls, verifying its identity as an audiovisual convergence region. These fMRI results suggest that vision-to-sound synesthetes have an exaggerated form of multisensory integration that occurs within the normal population.

Generalized linear and additive models for psychophysical data

What do such diverse paradigms as classification images, difference scaling and additive conjoint measurement have in common? We introduce a general framework that permits modeling and evaluating experiments covering a broad range of psychophysical tasks. Psychophysical data are considered within a signal detection model in which a decision variable, d, which is some function, f, of the stimulus conditions, S, is related to the expected probability of response, E[P], through a psychometric function, G: E[P] = G(f(d(S))). In many cases, the function f is linear, in which case the model reduces to E[P] = G(Xb), where X is a design matrix describing the stimulus configuration and b a vector of weights indicating how the observer combines stimulus information in the decision variable. By inverting the psychometric function, we obtain a Generalized Linear Model (GLM). We demonstrate how this model, which has previously been applied to calculation of signal detection theory parameters and fitting the psychometric function, is extended to provide maximum likelihood solutions for three tasks: classification image estimation, difference scaling and additive conjoint measurement. Within the GLM framework, nested hypotheses are easily set-up in a manner resembling classical analysis of variance. In addition, the GLM is easily extended to fitting and evaluating more flexible (nonparametric) models involving arbitrary smooth functions of the stimulus. In particular, this approach permits a principled approach to fitting smooth classification images.

MALE SEXUAL DYSFUNCTION IN SCHIZOPHRENIA: RELATIONSHIP WITH DRUG TREATMENT, PROLACTIN AND DRD2 GENOTYPE

Wagering contingent on a previous decision, or post-decision wagering, has recently been proposed to measure conscious awareness. Whilst intuitively appealing, it remains unclear whether economic context interacts with subjective confidence and how such interactions might impact on the measurement of awareness. Here we propose a signal detection model which predicts that advantageous wagers placed on the identity of preceding stimuli are affected by loss aversion, despite stimulus visibility remaining constant. This pattern of predicted results was evident in a psychophysical task where we independently manipulated perceptual and economic factors. Changes in wagering behaviour induced by changes in wager size were largely driven by changes in criterion, consistent with the model. However, for near-threshold stimuli, a reduction in wagering efficiency was also evident, consistent with an apparent but potentially illusory decrease in awareness of the stimulus. These findings challenge an assertion that post-decision wagering provides a direct index of subjective awareness.

Poster not available

Wagering contingent on a previous decision, or post-decision wagering, has recently been proposed to measure conscious awareness. Whilst intuitively appealing, it remains unclear whether economic context interacts with subjective confidence and how such interactions might impact on the measurement of awareness. Here we propose a signal detection model which predicts that advantageous wagers placed on the identity of preceding stimuli are affected by loss aversion, despite stimulus visibility remaining constant. This pattern of predicted results was evident in a psychophysical task where we independently manipulated perceptual and economic factors. Changes in wagering behaviour induced by changes in wager size were largely driven by changes in criterion, consistent with the model. However, for near-threshold stimuli, a reduction in wagering efficiency was also evident, consistent with an apparent but potentially illusory decrease in awareness of the stimulus. These findings challenge an assertion that post-decision wagering provides a direct index of subjective awareness.

Two components of oculomotor pursuit isolated by covariance based methods

We assessed covariation in performance between 55 individuals on various psychophysical tasks as well as an oculomotor pursuit task to a ramped stimulus. This analysis isolated two pursuit components of particular interest: 1) an early “latency” component consisting of latency to both presaccadic pursuit and the initial saccade, and 2) a later “accuracy” component consisting of accuracy of eye velocity during the 120ms following the first saccade. The early pursuit component was associated with three dynamic psychophysical tasks: motion detection (“Newsome” paradigm), velocity discrimination, and counterphase flicker identification. However, it was not associated with our two static psychophysical tasks: form detection and orientation discrimination. We propose that this pattern of results may reflect the presence of a high-level, temporal resolution of attention mechanism. It cannot reflect an entirely motion based mechanism because the counterphase flicker identification task does not evoke a motion percept, and moreover its thresholds are quite slow, ranging from 2 to 6 hz. It is unlikely that it reflects a generalized visual or temperamental mechanism because then one would expect the static psychophysical tasks to covary as well with this early stage of pursuit. The later, “accuracy” pursuit component was associated only with psychophysical velocity discrimination. Since this component was not associated with psychophysical motion detection, we propose that it reflects the presence of a mechanism devoted specifically to motion magnitude estimation, distinct from mechanisms devoted to the detection of motion.

Detecting patterns of covert attention shifts in psychophysical tasks using microsaccades

Detecting patterns of covert attention shifts in psychophysical tasks using microsaccades

Auditory and tactile integration in music meter perception.

Meter is a fundamental temporal structure of music. The perception of meter is typically inferred from the occurrence of accents in the music surface. Under normal listening conditions, listening to or playing music is usually accompanied by vibro‐tactile input which we hypothesize contributes to meter perception. Previous studies have shown that beat perception can occur via purely tactile stimulation. Whether vibro‐tactile stimulation can give rise to meter perception and how it interacts with auditory meter perception is unknown. Here we used accent occurrence and strength as cues to study meter perception in subjects performing auditory only, tactile only, and combined auditory‐tactile psychophysical discrimination tasks. We find that subjects can perceive meter through purely auditory only and tactile only stimulation. Furthermore, when stimuli were ambiguous, tactile stimulation was found to enhance meter perception when subjects were given weak auditory amplitude‐accented cues. Similarly, auditory stimulation enhanced meter perception when subjects were given weak tactile amplitude‐accented cues. These results indicate that meter perception is processed cross‐modally, and that auditory‐tactile integration plays an important role in the neural representation of temporal structures in music.

Relationship between physiological and psychoacoustical sensitivity to amplitude and frequency modulation.

Various researchers have found a correlation between the auditory steady state response (ASSR) and corresponding behavioral measurements such as speech recognition scores [e.g., Dimitrijevic et al. (2001)]. However, relatively few studies have examined the sensitivity to small changes in amplitude and frequency modulation depths. In the present study, it was hypothesized that physiological individual differences in sensitivity to amplitude and frequency modulation depths would be reflected in corresponding psychophysical measures. Auditory steady-state responses were collected in response to amplitude- and frequency-modulated pure tone carriers (500 and 3000 Hz) in normally hearing listeners over a range of modulation depths at several different modulation rates. Participants also completed a psychophysical task in which they were asked to detect the modulated tone in a two-interval forced choice testing paradigm. The relationships between the ASSR and the psychophysical performance will be discussed.

Discrimination of Vibrotactile Stimuli in the Rat Whisker System: Behavior and Neurometrics

Understanding the neural code underlying perception requires the mapping of physical stimulus parameters to both psychophysical decisions and neuronal responses. Here, we employed a novel psychophysical task in head-fixed rats to measure discriminability of vibrotactile whisker deflections. Rats could discriminate 90 Hz from 60 Hz pulsatile stimuli if stimulus intensity covaried with frequency. To pin down the physical parameters used by the rats to discriminate these vibrations, we manipulated stimulus amplitude to arrive at pairs of nondiscriminable stimuli. We found that vibrations matched in intensity (measured as mean absolute velocity), but differing in frequency, were no longer discriminable. Recordings of trigeminal ganglion neurons revealed that the distribution of neurometric sensitivities based on spike counts, but not interspike intervals, matched the rats' inability to discriminate intensity-matched stimuli. In conclusion, we suggest that stimulus mean absolute velocity, encoded in primary afferent spike counts, plays a prominent role for whisker-mediated perception.

Attention selects informative populations

Event Abstract Back to Event Attention selects informative populations Preeti Verghese1* and Alexander Wade1 1 Smith-Kettlewell Eye Research Institute, United States Motivation: Ideal observer theory predicts that observers use the most informative neural population for any particular task and that the identity of this neural population differs for different tasks. For orientation discrimination, Fischer information is highest in populations that have a preferred orientation tilted away from the target orientation as these neurons have orientation tuning functions that are most sensitive (steepest) in the region of the target orientation. For contrast discrimination, information is highest at the target orientation although the tuning is expected to be much weaker. Here we used source-imaged EEG to measure neural responses in humans while they performed two different tasks on the same stimuli. For each task, we asked whether our subjects attended to the most informative neural population as theory predicts. Methods: Observers performed either a contrast or an orientation discrimination task on one of two static, vertical targets, located 5∘ to the left and right of fixation. A cue indicated both the task type (contrast or orientation) and the location of the change (left or right). In order to probe the responses of neurons that were modulated attentionally but not driven directly by the target, we used frequency-tagged gratings within annuli that surrounded the target and flickered at 15 and 20 Hz on the left and right sides. These annuli were present throughout each 2-second trial. We used the frequency-tagged response amplitudes generated by these gratings to estimate the amplitude of the attentional modulation in the surrounded target region. Theory predicts that attention should preferentially modulate neurons tuned 20∘ away from the target in the orientation discrimination task, but not the contrast discrimination task. To test this, we used two different annulus grating orientations: one with the same orientation as the central, vertical target, and the other tilted 20∘ away. For each observer we collected high-density EEG data while they performed these tasks. We then used a minimum norm inverse procedure combined with realistic MR-derived head models and retinotopically-mapped visual areas to estimate cortical activity due to the grating annuli. To quantify the attentional modulation in each subject’s primary visual cortex (V1) we computed an attention modulation index (AMI): the difference between the attended response and unattended response normalized by the unattended response. Results: Attention to a spatial location clearly increased the amplitude of the response to the annulus surrounding that location. We observed these spatially-dependent amplitude modulations in both the contrast and orientation discrimination tasks. More importantly, the pattern of modulation depended on the task. For contrast discrimination both the 0∘ and 20∘ neural populations showed similar enhancements in area V1 consistent with the prediction that orientation tuning is weak in this task. For orientation discrimination, only the 20∘ population exhibited attentional modulation. These findings indicate that humans are able to attend selectively to the most informative neural population even at the level of primary visual cortex and that these populations change depending on the nature of the psychophysical task. Conference: Computational and Systems Neuroscience 2010, Salt Lake City, UT, United States, 25 Feb - 2 Mar, 2010. Presentation Type: Poster Presentation Topic: Poster session III Citation: Verghese P and Wade A (2010). Attention selects informative populations. Front. Neurosci. Conference Abstract: Computational and Systems Neuroscience 2010. doi: 10.3389/conf.fnins.2010.03.00202 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 03 Mar 2010; Published Online: 03 Mar 2010. * Correspondence: Preeti Verghese, Smith-Kettlewell Eye Research Institute, Rijeka, United States, preeti@ski.org Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Preeti Verghese Alexander Wade Google Preeti Verghese Alexander Wade Google Scholar Preeti Verghese Alexander Wade PubMed Preeti Verghese Alexander Wade Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Metamers of the ventral stream

Event Abstract Back to Event Metamers of the ventral stream Jeremy Freeman1* and Eero P. Simoncelli2 1 New York University , Center for Neural Science, United States 2 New York University , United States How is image structure encoded in the extrastriate ventral visual pathway? Direct characterization of the stimulus selectivity of individual extrastriate cells has proven difficult. However, one robust population-level property of all visual areas is that receptive field sizes grow with eccentricity. It has also been reported (Gattass et al., 1988) that the rate of growth increases along the ventral stream. We hypothesize that this successive increase in pooling region size causes information loss. A well known example occurs in the retina, where spatial pooling in the periphery means that high spatial frequency information is lost. In general, stimuli that differ only in terms of information discarded by the visual system will be indistinguishable to a human observer. Such stimuli are called metamers. Here, we probe the population-level computations of the ventral stream using novel metameric stimuli. Starting from any prototype image, we generate stimuli that match in terms of the responses of a simple model for extrastriate ventral computation. The model is based on measurements previously used to characterize visual texture (Portilla & Simoncelli, 2000). The model decomposes an image using a bank of V1-like filters tuned for local orientation and spatial frequency, computing both simple and complex-cell responses. Extrastriate responses are then computed by taking pairwise products amongst these V1 responses, and averaging within overlapping spatial regions that grow with eccentricity. Stimuli are generated by using gradient descent to adjust a random (white noise) image to match the model responses of the original prototype. Previous work showed that the same statistics, averaged over an entire image, allow for the analysis and synthesis of homogenous visual textures. If this model accurately reflects representations in early extrastriate areas, then images synthesized to produce identical model responses should be metameric to a human observer. For each of several natural images and pooling region sizes, we generate multiple samples that are statistically-matched but otherwise as random as possible. We use a standard psychophysical task to measure observers’ ability to discriminate between image samples, as a function of the rate at which the statistical pooling regions grow with eccentricity. When image samples are statistically matched within small pooling regions, observers perform at chance (50%), failing to notice substantial differences in the periphery. When images are matched within larger pooling regions, discriminability approaches 100%. We fit the psychometric function to estimate the pooling region over which the observer estimates statistics. The result is consistent with receptive field sizes in macaque mid-ventral areas (particularly V2). Our model also fully instantiates a recently proposed explanation (Balas et al., 2009) of the phenomenon of "visual crowding", in which humans fail to recognize a peripheral target object surrounded by background clutter. In our model, crowding occurs because multiple objects fall within the same pooling region and the model responses cannot uniquely identify the target object. We synthesize images that are metameric to classic crowding stimuli (e.g. groups of letters), and find that stimulus configurations that produce crowding yield synthesized images with jumbled, unidentifiable objects. Conference: Computational and Systems Neuroscience 2010, Salt Lake City, UT, United States, 25 Feb - 2 Mar, 2010. Presentation Type: Oral Presentation Topic: Oral presentations Citation: Freeman J and Simoncelli EP (2010). Metamers of the ventral stream. Front. Neurosci. Conference Abstract: Computational and Systems Neuroscience 2010. doi: 10.3389/conf.fnins.2010.03.00053 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 18 Feb 2010; Published Online: 18 Feb 2010. * Correspondence: Jeremy Freeman, New York University, Center for Neural Science, New York, United States, jeremy@carbonplan.org Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Jeremy Freeman Eero P Simoncelli Google Jeremy Freeman Eero P Simoncelli Google Scholar Jeremy Freeman Eero P Simoncelli PubMed Jeremy Freeman Eero P Simoncelli Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Effects of loss aversion on post-decision wagering: Implications for measures of awareness

Wagering contingent on a previous decision, or post-decision wagering, has recently been proposed to measure conscious awareness. Whilst intuitively appealing, it remains unclear whether economic context interacts with subjective confidence and how such interactions might impact on the measurement of awareness. Here we propose a signal detection model which predicts that advantageous wagers placed on the identity of preceding stimuli are affected by loss aversion, despite stimulus visibility remaining constant. This pattern of predicted results was evident in a psychophysical task where we independently manipulated perceptual and economic factors. Changes in wagering behaviour induced by changes in wager size were largely driven by changes in criterion, consistent with the model. However, for near-threshold stimuli, a reduction in wagering efficiency was also evident, consistent with an apparent but potentially illusory decrease in awareness of the stimulus. These findings challenge an assertion that post-decision wagering provides a direct index of subjective awareness.

The role of vertical mirror symmetry in visualshape detection

The goal of our study is a better understanding of the role of vertical mirror symmetry in perceptual grouping. With a simple psychophysical task and a set of controlled stimuli, we investigated whether vertical mirror symmetry acts as a cue in figure-ground segregation. We asked participants to indicate which of two sequentially presented Gabor arrays contained a visual shape. The shape was defined by a subset of Gabor elements positioned along the outline of an unfamiliar shape. By adding orientation noise to these Gabor elements, the shape percept became less salient. Across the different noise levels, symmetric shapes were easier to detect than asymmetric ones. This finding indicates that vertical mirror symmetry is indeed used as a cue in perceptual grouping.

Improved classification images with sparse priorsin a smooth basis

Classification images provide compelling insight into the strategies used by observers in psychophysical tasks. However, because of the high-dimensional nature of classification images and the limited quantity of trials that can practically be performed, classification images are often too noisy to be useful unless denoising strategies are adopted. Here we propose a method of estimating classification images by the use of sparse priors in smooth bases and generalized linear models (GLMs). Sparse priors in a smooth basis are used to impose assumptions about the simplicity of observers' internal templates, and they naturally generalize commonly used methods such as smoothing and thresholding. The use of GLMs in this context provides a number of advantages over classic estimation techniques, including the possibility of using stimuli with non-Gaussian statistics, such as natural textures. Using simulations, we show that our method recovers classification images that are typically less noisy and more accurate for a smaller number of trials than previously published techniques. Finally, we have verified the efficiency and accuracy of our approach with psychophysical data from a human observer.

Psychophysical Acting: An Intercultural Approach after Stanislavski (review)

Reviewed by: Psychophysical Acting: An Intercultural Approach after Stanislavski Kevin McFillen Psychophysical Acting: An Intercultural Approach after Stanislavski. By Phillip B. Zarrilli (DVD-ROM by Peter Hulton). New York: Routledge, 2008; pp. xiii + 255. $39.95 paper. Phillip Zarrilli's Psychophysical Acting: An Intercultural Approach after Stanislavski provides not only a grounding in Zarrilli's more than three decades of experience with intercultural modes of performance, but also a substantial overview of the history and development of psychophysical acting processes and their application to both actor training and practical production work. Part 1, "What Is the Actor's Work?," begins with a historical overview of the development of the notion of the psychophysical as a means of describing the interaction between body and mind, and in particular Stanislavski's application of the term "to describe an approach to Western acting focused equally on the actor's psychology and physicality applied to textually based character acting" (13). Zarrilli traces the development of this concept of acting as a psychophysical process from the legacy of Stanislavski to his own experience training in various methods of physical performance and martial arts, including kathakali dance-drama, the related Indian martial art of kalarippayattu, the ancient Chinese martial art of Wu-style taiqiquan, and the hatha tradition of yoga, and provides examples of each through the accompanying DVD-ROM by Peter Hulton. In the final chapter of part 1, Zarrilli moves to examining the effects of the psychophysical nature of acting on acting's theoretical underpinnings, exploring acting as the embodiment of an actor's modes of experience, and drawing together the teachings gleaned from his experiences with kathakali, kalarippayattu, taiqiquan, and hatha yoga with critical theories of embodiment and performance as a means of grounding the theories and exercises later described in part 2, "Work on Oneself." Part 2 begins with an in-depth history and examination of the primary source traditions of kalarippayattu, taiqiquan, and hatha yoga that inform Zarrilli's understanding of the psychophysical process of acting, before moving to a structured program of study in chapter 5, "The Psychophysical Actor's 'I Can.'" This program walks the reader through Zarrilli's primary strategies and exercises for both cultivating greater awareness and attempting to move beyond the experience of the body and mind as separate entities within the moment of performance. While largely theoretical and philosophical in nature, this program serves as a useful model for bridging the gap between the cultural and historical examination of the source traditions behind Zarrilli's work and the "structured improvisations" he describes in the final chapter of part 2, "Exercises for 'Playing' In-between." Zarrilli defines these exercises as "a set of very simple psychophysical tasks organized into increasingly complex rule-based structures played in a workshop setting" (100), and are helpfully supplemented for greater clarity by examples on the accompanying DVD-ROM. Zarrilli devotes part 3 to five in-depth case studies of productions from his own work as well as the work of related performance groups. First is Zarrilli's The Beckett Project, a series of productions produced as part of a nine-month project applying psychophysical training techniques to the works of Samuel Beckett (124), second is Ota Shogo's production of The Water Station created with the Theatre of Transformation (Tenkei Gekijo) (144), third is Speaking Stones, a piece commissioned from Zarrilli by the Austrian Theatre Asou (174), fourth is Zarrilli's production of Sarah Kane's 4:48 Psychosis, workshopped at the University of Exeter and fully mounted at the Korean National University of Arts in Seoul (189), and last is Zarrilli's production of Martin Crimp's Attempts on Her Life, again workshopped at the University of Exeter before receiving a full production at the Esplanade Theatre Studio in Singapore (201). Psychophysical Acting is ultimately somewhat limited by its immense scope, seeking to provide the reader with not only the aforementioned background into the history, philosophy, and practice of both psychophysical acting and the source traditions of Zarrilli's work, but with the practical tools and production documentation covered in the latter sections of the book as well. Equally, despite the enormous benefit to the text's accessibility provided...

No evidence for impaired perception of biological motion in adults with autistic spectrum disorders

A central feature of autistic spectrum disorders (ASDs) is a difficulty in identifying and reading human expressions, including those present in the moving human form. One previous study, by Blake et al. (2003), reports decreased sensitivity for perceiving biological motion in children with autism, suggesting that perceptual anomalies underlie problems in social cognition. We revisited this issue using a novel psychophysical task. 16 adults with ASDs and 16 controls were asked to detect the direction of movement of human point-light walkers which were presented in both normal and spatially scrambled forms in a background of noise. Unlike convention direction discrimination tasks, in which walkers walk 'on the spot' while facing left or right, we added translatory motion to the stimulus so that the walkers physically moved across the screen. Therefore, while a cue of coherent, translatory motion was available in both the normal and scrambled walker forms, the normal walker alone contained information about the configuration and kinematics of the human body. There was a significant effect of walker type, with reduced response times and error when the normal walker was present. Most importantly, these improvements were the same for both participant groups, suggesting that people with ASDs do not have difficulty integrating local visual information into a global percept of the moving human form. The discrepancy between these and previous findings of impaired biological motion perception in ASDs are discussed with reference to differences in the age and diagnosis of the participants, and the nature of the task.

Subcortical differentiation of stop consonants relates to reading and speech-in-noise perception

Children with reading impairments have deficits in phonological awareness, phonemic categorization, speech-in-noise perception, and psychophysical tasks such as frequency and temporal discrimination. Many of these children also exhibit abnormal encoding of speech stimuli in the auditory brainstem, even though responses to click stimuli are normal. In typically developing children the auditory brainstem response reflects acoustic differences between contrastive stop consonants. The current study investigated whether this subcortical differentiation of stop consonants was related to reading ability and speech-in-noise performance. Across a group of children with a wide range of reading ability, the subcortical differentiation of 3 speech stimuli ([ba], [da], [ga]) was found to be correlated with phonological awareness, reading, and speech-in-noise perception, with better performers exhibiting greater differences among responses to the 3 syllables. When subjects were categorized into terciles based on phonological awareness and speech-in-noise performance, the top-performing third in each grouping had greater subcortical differentiation than the bottom third. These results are consistent with the view that the neural processes underlying phonological awareness and speech-in-noise perception depend on reciprocal interactions between cognitive and perceptual processes.

Enhanced Visual Motion Perception in Major Depressive Disorder

Major depressive disorder (MDD) is a mood disorder that is not traditionally considered to affect the visual system. However, recent findings have reported decreased cortical levels of the inhibitory neurotransmitter GABA in occipital cortex. To explore possible functional consequences of MDD on visual processing, we applied a psychophysical visual motion processing task in which healthy young adults typically exhibit impaired perceptual discrimination of large high-contrast stimuli. It has been suggested that this phenomenon, spatial suppression, is mediated by GABAergic center-surround antagonism in visual pathways. Based on previous findings linking MDD to occipital GABA dysfunction, we hypothesized that MDD patients would exhibit decreased spatial suppression, leading to the counterintuitive hypothesis of better psychophysical performance. Indeed, motion perception for typically suppressed stimuli was enhanced in patients with MDD compared with age-matched controls. Furthermore, the degree of spatial suppression correlated with an individual's illness load; patients with greater lifetime duration of depression exhibited the least spatial suppression and performed the best in the high-contrast motion discrimination task. Notably, this decrease in spatial suppression persisted beyond recovery and without the confound of acute illness or treatment; all patients had been clinically recovered and unmedicated for several months at the time of testing, suggesting that depression has ubiquitous consequences that may persist long after mood symptoms have receded. This finding raises the possibility that spatial suppression may represent a sensitive endophenotypic marker of trait vulnerability in MDD.

The influence of temporal resolution power and working memory capacity on psychometric intelligence

According to the temporal resolution power (TRP) hypothesis, higher TRP as reflected by better performance on psychophysical timing tasks accounts for faster speed of information processing and increased efficiency of information processing leading to better performance on tests of psychometric intelligence. An alternative explanation of individual differences in psychometric intelligence highlights individual differences in working memory (WM) capacity which has been found to be closely associated with psychometric intelligence. A latent variable approach was applied on the data of 200 participants ranging in age from 18 to 30 years and spanning a large range of levels of psychometric intelligence. Functional relationships were examined among TRP, WM capacity, as well as reasoning and speed of processing as two important aspects of psychometric intelligence. As predicted by the TRP hypothesis, the relation between TRP and psychometric intelligence was mediated by WM capacity supporting the view that higher TRP leads to better coordinated mental operations which, in turn, result in higher psychometric intelligence. The results are discussed against the background that WM capacity and psychometric reasoning are hardly dissociable from each other and that the specific factors limiting WM capacity and accounting for the mediation effect need to be identified in future research.

Contrast Insensitivity: The Critical Immaturity in Infant Visual Performance

This is a targeted review of the critical immaturities limiting psychophysical luminance contrast detection in human infants. Three-month-old infants are 50 times less sensitive to contrast than adults are. Rod experiments suggest that early-stage immaturities, like the short length of infant rod outer segments, have only a modest direct effect on infant visual performance. Infant contrast sensitivity may resemble adult extrafoveal sensitivity, because the foveal cones of the neonate are immature and may not generate strong enough responses to mediate visual performance. This use of the extrafoveal retina reduces the high-spatial frequency end of the infant contrast sensitivity function (CSF), contributing to poor infant resolution acuity. The remaining difference between infant and adult CSFs may be a simple overall reduction in infant sensitivity. The maximum of the infant CSF increases proportionately with age, and may be numerically near the infant's age in weeks. Contrast discrimination experiments indicate that the critical immaturity that limits infant contrast sensitivity is a mid-level phenomenon, occurring before the site of the contrast gain control. For example, the infant ascending visual pathway might be limited by large amounts of intrinsic noise. These results suggest that there is little effect of inattentiveness to the psychophysical task by ostensibly alert infant patients or subjects. The clinician or researcher can interpret behavioral measurements of infant visual performance with confidence.