Task switching: a PDP model

When subjects switch between a pair of stimulus-response tasks, reaction time is slower on trial N if a different task was performed on trial N - 1. We present a parallel distributed processing (PDP) model that simulates this effect when subjects switch between word reading and color naming in response to Stroop stimuli. Reaction time on "switch trials" can be slowed by an extended response selection process which results from (a) persisting, inappropriate states of activation and inhibition of task-controlling representations; and (b) associative learning, which allows stimuli to evoke tasks sets with which they have recently been associated (as proposed by Allport & Wylie, 2000). The model provides a good fit to a large body of empirical data, including findings which have been seen as problematic for this explanation of switch costs, and shows similar behavior when the parameters are set to random values, supporting Allport and Wylie's proposal.     

The interpolation of object and surface structure

One of the main theoretical challenges of vision science is to explain how the visual system interpolates missing structure. Two forms of visual completion have been distinguished on the basis of the phenomenological states that they induce. Modal completion refers to the formation of visible surfaces and/or contours in image regions where these properties are not specified locally. Amodal completion refers to the perceived unity of objects that are partially obscured by occluding surfaces. Although these two forms of completion elicit very different phenomenological states, it has been argued that a common mechanism underlies modal and amodal boundary and surface interpolation (the "identity hypothesis"; Kellman & Shipley, 1991; Kellman, 2001). Here, we provide new data, demonstrations, and theoretical principles that challenge this view. We show that modal boundary and surface completion processes exhibit a strong dependence on the prevailing luminance relationships of a scene, whereas amodal completion processes do not. We also demonstrate that the shape of interpolated contours can change when a figure undergoes a transition from a modal to an amodal appearance, in direct contrast to the identity hypothesis. We argue that these and previous results demonstrate that modal and amodal completion do not result from a common interpolation mechanism.     

Arrows of time in infancy: the representation of temporal-causal invariances

Many transformations that take place over time can only occur in one temporal direction, and adults are highly sensitive to the differences between forward and backward presentations of such events. In seven experiments using two selective-looking paradigms, 4- and 8-month-olds were shown forward and backward videotapes of events involving the effects of gravity on liquids and solid objects and of the separation of whole objects into pieces. Four-month-olds showed a significant preference for the forward version of liquid pouring from a beaker to a glass. Eight-month-olds looked longer at the forward versions of this and four other gravity-related events but showed no directional preferences for the separation events. Several experiments indicate that longer looking at the forward versions of the gravity stimuli is not a product of attraction to specific perceptual features of the stimuli. A model based on the development of representations of types of events is presented and evaluated.     

Competition, inhibition, and semantic judgment errors in Parkinson's disease

Semantic processing errors are symptoms of an up-regulation (schizophrenia) or degradation (Parkinsonism) of dopaminergic pathways. A recent connectionist model attributed errors in the schizophrenic processing of context to increased gain in competitive neural processes. This study extends this "gain hypothesis" by comparing the sensitivity to reduced gain of a simulation of semantic route activation to characteristic semantic judgment errors made by Parkinson's patients in an open search task. Under normal gain conditions, the dominant sense of polysemous words "wins" through competition and lateral inhibition at the word sense level (beta(inh)). For words with very different sense frequencies, decreasing gain by increasing beta(inh) resulted in the dominant word sense winning; however, for words with similar sense frequencies, increasing beta(inh) resulted in the dominant word sense winning only for low to moderate values. At high levels, no clear winner emerged after 200 epochs, with the least dominant sense reaching the maximum activation value. These results are discussed in the context of the Yerkes-Dodson Law, which may provide a theoretical basis for understanding normal and impaired semantic performance in catecholaminergic disorders.     

The relationship between prosody and breathing in spontaneous discourse

This article is concerned with the role of prosody in discourse. Three experiments explored the relationship between inspiration, declination, and syntactic boundaries in normal and RHD participants. Fundamental frequency and intensity were measured at the beginning and end of breath units excised from conversational samples. The results revealed evidence of declination of intensity in all samples measured. However, resetting of fundamental frequency was observed only in the samples of normal participants and then only when a breath coincided with the beginning of a sentence. The results suggest that resetting and declination play separate roles in discourse parsing.     

Dissociating prelexical and postlexical processing of affective information in the two hemispheres: effects of the stimulus presentation format

Using a lexical decision task, the authors investigated whether brain asymmetries in the detection of emotionally negative semantic associations arise only at a perceptually discriminative stage at which lexical analysis is accurate or can already be found at crude and incomplete levels of perceptual representation at which word-nonword discrimination is based solely on guessing. Emotionally negative and neutral items were presented near perceptual threshold in the left and right visual hemifields. Word-nonword discrimination performance as well as the bias to classify a stimulus as a "word" (whether or not it actually is a word) were assessed for a normal, horizontal stimulus presentation format (Experiment 1) and for an unusual, vertical presentation format (Experiment 2). Results show that while the two hemispheres are equally able to detect affective semantic associations at a prelexical processing stage (both experiments), the right hemisphere is superior at a postlexical, perceptually discriminative stage (Experiment 2). Moreover, the findings suggest that only an unusual, nonoverlearned stimulus presentation format allows adequate assessment of the right hemisphere's lexical-semantic skills.     

Long-term efficacy of exercise across diagnostically heterogenous mental disorders and the mediating role of affect regulation skills

BackgroundExercise interventions are efficacious in reducing disorder-specific symptoms in various mental disorders. However, little is known about long-term transdiagnostic efficacy of exercise across heterogenous mental disorders and the potential mechanisms underlying treatment effects.MethodsPhysically inactive outpatients, with depressive disorders, anxiety disorders, insomnia or attention deficit hyperactivity disorder were randomized to a standardized 12-week exercise intervention, combining moderate exercise with behavior change techniques (BCTs) (n = 38), or a passive control group (n = 36). Primary outcome was global symptom severity (Symptom Checklist-90, SCL-90-R) and secondary outcomes were self-reported exercise (Physical Activity, Exercise, and Sport Questionnaire), exercise-specific affect regulation (Physical Activity-related Health Competence Questionnaire) and depression (SCL-90-R) assessed at baseline (T1), post-treatment (T2) and one year after post-treatment (T3). Intention-to-treat analyses were conducted using linear mixed models and structural equations modeling.ResultsFrom T1 to T3, the intervention group significantly improved on global symptom severity (d = −0.43, p = .031), depression among a depressed subsample (d = −0.62, p = .014), exercise (d = 0.45, p = .011) and exercise-specific affect regulation (d = 0.44, p = .028) relative to the control group. The intervention group was more likely to reveal clinically significant changes from T1 to T3 (p = .033). Increases in exercise-specific affect regulation mediated intervention effects on global symptom severity (ß = −0.28, p = .037) and clinically significant changes (ß = −0.24, p = .042).ConclusionsThe exercise intervention showed long-term efficacy among a diagnostically heterogeneous outpatient sample and led to long-lasting exercise behavior change. Long-term increases in exercise-specific affect regulation within exercise interventions seem to be essential for long-lasting symptom reduction.     

Predicting dyslexia at 8 years of age using neonatal brain responses

Auditory event-related potentials recorded at birth to speech and nonspeech syllables from six scalp electrodes discriminated between newborn infants who 8 years later would be characterized as dyslexic, poor, or normal readers. These findings indicate that reading problems can be identified and possible interventions undertaken up to 9 years earlier than is currently possible.     

Interhemispheric effects of simulated lesions in a neural model of single-word reading

A neural model consisting of paired cerebral hemispheric regions interacting via homotopic callosal connections was trained to generate pronunciations for 50 monosyllabic words. Lateralization of this task occurred readily when different underlying cortical asymmetries were present. Following simulated focal cortical lesions of systematically varied sizes, acute changes in the distribution of cortical activation were found to be most consistent with experimental data when interhemispheric interactions were assumed to be excitatory. During subsequent recovery, the contribution of the unlesioned hemispheric region to performance improvement was a function of both the amount of preexisting lateralization and the side and size of the lesion. These results are discussed in the context of unresolved issues concerning the mechanisms underlying language lateralization, the nature of interhemispheric interactions, and the role of the nondominant hemisphere in recovery from adult aphasia.     

Language localization in cases of left temporal lobe arachnoid cyst: evidence against interhemispheric reorganization

We investigated whether left-hemisphere arachnoid cysts lead to reorganization of the language function using PET. A group analysis demonstrated that patients showed no more right-hemisphere activation than a matched control group. Several patients had clear language localizations in the left hemisphere during language comprehension; none of the patients showed right-hemisphere activation. We conclude that left-hemisphere tissue must suffer considerable compromise before reorganization of language into the right hemisphere becomes necessary. Language activations within the left hemisphere are clearly displaced. This is consistent with mere physical displacement in some patients rather than reorganization within the left hemisphere; in others intrahemispheric reorganization cannot be excluded.