Visual receptive fields and clustering

A pattern recognition technique—clustering—has been used to analyze and evaluate meaningful characteristics of visual receptive fields in the frog tectum. The fields were mapped either by an automatic scanning technique or by a response-feedback method called ALOPEX. The data were then analyzed by the clustering technique, which separates the receptive field into isoresponse regions. The latter can be checked on line by stimulating the eye with each cluster and with combinations of clusters. In this way, existing nonlinearities can be checked objectively.     

Corners,receptive fields,and visually evoked cortical potentials

Alternating stimuli with herringbone patterns were used to obtain visually evoked cortical potentials (VECPs) from three human Ss. Two sets of stimulus patterns were used, one with sharp corners and one with the corners rounded off. Each set ranged in angularity from 180 to 45 deg in 45-deg steps. Results showed that: (a)VECP response amplitude was greatest for the 90-deg-corner pattern, (b) response amplitude was greater for the 45-deg-corner pattern than for the 135-deg-corner pattern, and (c) cornered and rounded patterns evoked responses of greater amplitude than those evoked by the straight (180-deg) patterns. Also, the peak latency of responses to cornered patterns was shorter than that of responses to rounded and straight patterns.     

Detecting gaps with and without attention: Further evidence for attentional receptive fields

In four experiments participants were instructed to detect and localise a gap on a small vertical line. When the line was presented at the periphery, inattention produced a tendency to report broken lines as solid ones and also produced a substantial increase in coarse localisation errors. The results support the hypothesis (Tsal & Shalev, 1996) that the unattended visual field is composed of large attentional receptive fields (ARFs) within which there is no spatial resolution. A partial stimulation of such an ARF, by the broken line's inner ends producing the gap, signals the activation of the entire ARF resulting in the perceptual closure of the gap.     

Attentional attraction of receptive fields can explain spatial and temporal effects of attention

A multitude of attentional effects were found at both the neural and behavioural levels of perception; however, the nature of the attentional mechanism is an unsettled issue. It is typically assumed that the fundamental impact of attention is enhancement of neuronal responses, but some attentional effects are difficult to explain by such gain modulations. Here we offer a different view: We suggest that the most fundamental impact of attention is the attraction (shift) of receptive fields towards the attended location. We further show, both conceptually and by model simulations, that this attraction of receptive fields can explain a diverse range of attentional effects, spatial as well as temporal, linking physiological measurements at the unit level with psychophysical observations (e.g., enhanced contrast sensitivity, enhanced spatial resolution, the Mexican-hat profile of attention, prolonged perceived duration, prior entry, degraded temporal resolution).     

Effects of receptive language training on receptive and expressive language development

The effects of a six-month training program in receptive language on receptive and expressive language development were investigated. Developmentally retarded preschoolers were pretested and posttested on one standardized test of receptive language and two tests of expressive language. Both the training and control groups participated in a preschool program. In addition, the training group received a two-sequence training program: (1) reinforcement for matching responses to modeling cues and accompanying verbal requests, and (2) reinforcement for appropriate responses to verbal requests alone. The training group demonstrated a significant increase in appropriate responses to verbal request over base-rate performance after the training and also demonstrated a significantly improved posttest performance on one test of expressive language as compared to the control group.The authors wish to thank Mrs. Helen Huggins and the staff of the Aid to Retarded Children's Preschool Training Center, San Francisco, California, for their assistance in this study. A modified version of this paper was presented at the Gatlinburg Conference on Mental Retardation, March, 1974, Gatlinburg, Tennessee.     

Functional neuroimaging in neurology and psychiatry

How can functional neuroimaging be applied to clinical neurology and psychiatry? This article reviews selected contributions of functional neuroimaging to the clinical neurosciences. We review selected technical aspects of positron emission tomography, single photon emission tomography, and functional magnetic resonance imaging with a focus on the relative strengths and weaknesses of these techniques. Consumers of functional neuroimaging research are encouraged to consider the limitations of imaging techniques and theoretical pitfalls of cognitive task design when interpreting results of functional imaging studies. Then, we selectively review the contributions of functional neuroimaging to neurology and psychiatry, including the areas of epilepsy, stroke, chronic pain, schizophrenia, depression, and obsessive-compulsive disorder. Future directions of functional neuroimaging research are offered, with the emphasis that the best conclusions are informed by a convergence of research from functional neuroimaging, neurophysiological, and lesion studies.     

Magnetoencephalography in pediatric neuroimaging

Neural currents give rise to electroencephalogram (EEG) and magnetoencephalogram (MEG). MEG has selective sensitivity to tangential currents (from fissural cortex), and less distorted signals compared with EEG. A major goal of MEG is to determine the location and timing of cortical generators for event‐related responses, spontaneous brain oscillations or epileptiform activity. MEG provides a spatial accuracy of a few mm under optimal conditions, combined with an excellent submillisecond temporal resolution, which together enable spatiotemporal tracking of distributed neural activities, e.g. during cognitive tasks or epileptic discharges. While the present focus of pediatric MEG is on tailored epilepsy surgery, the complete noninvasiveness of MEG also provides unlimited possibilities to study the brain functions of healthy and developmentally deviant children.     

Integrating cognitive psychology, neurology and neuroimaging

In the last decade, there has been a dramatic increase in research effectively integrating cognitive psychology, functional neuroimaging, and behavioral neurology. This new work is typically conducting basic research into aspects of the human mind and brain. The present review features as examples of such integrations two series of studies by the author and his colleagues. One series, employing object recognition, mental motor imagery, and mental rotation paradigms, clarifies the nature of a cognitive process, imagined spatial transformations used in shape recognition. Among other implications, it suggests that when recognizing a hand's handedness, imagining one's body movement depends on cerebrally lateralized sensory-motor structures and deciding upon handedness depends on exact match shape confirmation. The other series, using cutaneous, tactile, and auditory pitch discrimination paradigms, elucidates the function of a brain structure, the cerebellum. It suggests that the cerebellum has non-motor sensory support functions upon which optimally fine sensory discriminations depend. In addition, six key issues for this integrative approach are reviewed. These include arguments for the value and greater use of: rigorous quantitative meta-analyses of neuroimaging studies; stereotactic coordinate-based data, as opposed to surface landmark-based data; standardized vocabularies capturing the elementary component operations of cognitive and behavioral tasks; functional hypotheses about brain areas that are consistent with underlying microcircuitry; an awareness that not all brain areas implicated by neuroimaging or neurology are necessarily directly involved in the associated cognitive or behavioral task; and systematic approaches to integrations of this kind.     

Generative models, brain function and neuroimaging

The representational capacity and inherent function of any neuron, neuronal population or cortical area in the brain is dynamic and context-sensitive. Functional integration, or interactions among brain systems, that employ driving (bottom up) and backward (top-down) connections, mediate this adaptive and contextual specialisation. A critical consequence is that neuronal responses, in any given cortical area, can represent different things at different times. This can have fundamental implications for the design of brain imaging experiments and the interpretation of their results. Our arguments are developed under generative models of brain function, where higher-level systems provide a prediction of the inputs to lower-level regions. Conflict between the two is resolved by changes in the higher-level representations, which are driven by the ensuing error in lower regions, until the mismatch is "cancelled". From this perspective the specialisation of any region is determined both by bottom-up driving inputs and by top-down predictions. Specialisation is therefore not an intrinsic property of any region but depends on both forward and backward connections with other areas. Because the latter have access to the context in which the inputs are generated they are in a position to modulate the selectivity or specialisation of lower areas. The implications for classical models (e.g., classical receptive fields in electrophysiology, classical specialisation in neuroimaging and connectionism in cognitive models) are severe and suggest these models may provide incomplete accounts of real brain architectures. Here we focus on the implications for cognitive neuroscience in the context of neuroimaging.     

Functional neuroimaging of autistic disorders

Functional neuroimaging methods hold promise for elucidating the neurobiology of autistic disorders, yet they present difficult practical and scientific challenges when applied to these complex and heterogeneous syndromes. Single-state studies of brain metabolism and blood flow thus far have failed to yield consistent findings, but suggest considerable variability in regional patterns of cerebral synaptic activity. Patients with idiopathic autism are less likely to show abnormalities than are patients with comorbid illness or epilepsy. Activation studies have begun to suggest alterations in brain organization for language and cognition. Neurotransmitter studies using positron emission tomography (PET) suggest abnormalities of serotonergic and dopaminergic function. Studies using magnetic resonance spectroscopy (MRS) have begun to document metabolic deficits in the frontal cortex and cerebellum. A single study using magnetoencephalography suggests a high incidence of epileptiform activity in children with autistic regression. Research needs include well-controlled developmental studies, particularly of young subjects and relatively homogeneous subgroups, which balance scientific rigor with ethical constraints. Investigations of the serotonergic and dopaminergic systems, limbic-based memory and emotional systems, and the role of epileptiform activity in autism represent priorities for future research.     

The social brain meets neuroimaging

Recent neuroimaging studies in humans have indicated that individual differences in social network size correlate with amygdala volume and the volume of brain regions associated with theory of mind. A new article demonstrates that this is also true for monkeys. Taken together, these findings provide crucial support for the social brain hypothesis.     

Functional neuroimaging of autobiographical memory

Functional neuroimaging studies of autobiographical memory have grown dramatically in recent years. These studies are important because they can investigate the neural correlates of processes that are difficult to study using laboratory stimuli, including: (i) complex constructive processes, (ii) recollective qualities of emotion and vividness, and (iii) remote memory retrieval. Constructing autobiographical memories involves search, monitoring and self-referential processes that are associated with activity in separable prefrontal regions. The contributions of emotion and vividness have been linked to the amygdala and visual cortex respectively. Finally, there is evidence that recent and remote autobiographical memories might activate the hippocampus equally, which has implications for memory-consolidation theories. The rapid development of innovative methods for eliciting personal memories in the scanner provides the opportunity to delve into the functional neuroanatomy of our personal past.     

Methodological issues in pediatric neuroimaging

The emergence of new technologies to study brain function in vivo has resulted in an explosion of interest in cognitive neuroscience within the last ten years. While most research in functional neuroimaging has been geared toward adult normal volunteers, the development of functional magnetic resonance imaging (fMRI) has made it possible to study neural development in normal children, as well as those with developmental disorders. This technology provides an unprecedented opportunity to expand our knowledge of brain function throughout childhood. A variety of technological, experimental, and practical difficulties are amplified when imaging children. This paper reviews some of the more challenging theoretical and practical concerns and provides suggestions for their management.     

Autism and receptive dysphasia: Evaluation of comparative studies

Ten different studies comparing children with autism and receptive dysphasia are reviewed. Most of the studies aimed to characterize autism as a language disorder. The representativity of the samples are discussed according to heterogeneity of the autistic and dysphatic populations, and sex and social class distributions. Group differences and similarities are listed and discussed according to sample selection and matching procedures, age and sex distribution, social class membership, and the defining criteria of the two illnesses. It is concluded that the studies do not fullfill their aim, and that the project of comparing dysphatic and autistic children seems unfruitful. Group differences which seem unconnected with methodological difficulties, selection procedure, or group defining criteria, were found in parental background, use of gestures, articulation, and reading.     

Expressive and receptive language skills of temperamentally shy preschoolers

Although shy children speak less in social situations, the extent to which their language skills fall behind those of their more outgoing peers remains unclear. We selected 22 temperamentally shy and 22 non‐shy children from a larger group of 400 4‐year‐old children who were prescreened for temperamental shyness by maternal report, using the Colorado Childhood Temperament Inventory (CCTI). We then compared the two groups on widely used measures that index expressive and receptive language skills. We found that, although the temperamentally shy children scored lower on both expressive and receptive language skills compared with their non‐shy counterparts, they were nonetheless performing at their age equivalency. The non‐shy children, however, were performing significantly above their age level on expressive and receptive language skills. These findings suggest that the development of normal language skills is not compromised in temperamentally shy preschoolers. Copyright © 2004 John Wiley & Sons, Ltd.     

Ethics of neuroimaging in pediatric development

Neuroimaging in pediatrics is accompanied by all the ethical dilemmas associated with neuroimaging in adults, magnified significantly. The defining characteristics of childhood make working ethically with the population particularly problematic. Children have not developed the rational capabilities necessary to make informed decisions and the variability and change associated with development contribute to heightened risks and/or benefits of any procedure and limit interpretation of data. As a consequence, fewer pediatric than adult neuroimaging research studies have been done, further limiting general knowledge of the field. Significant strides have been made just within the past few years with the collection of normative data sets of healthy children. Recommendations on how to proceed with pediatric neuroimaging studies while ensuring ethical treatment of the participants are presented.