Daniel J. Weeks

Salient-features coding in the translation between orthogonal stimulus and response dimensions

The present study evaluated whether recent theoretical advances regarding cognitive coding render a translation-based account viable for orthogonal stimulus-response arangements

Inferring online and offline processing of visual feedback in target-directed movements from kinematic data

Vision plays an important role in the planning and execution of target-directed aiming movements. In this review, we highlight the limitations that exist in detecting visual regulation of limb trajectories from traditional kinematic analyses such as the identification of discontinuities in velocity and acceleration. Alternative kinematic analyses that involve examining variability in limb trajectories to infer visual control processes are evaluated. The basic assumption underlying these methods is that noise exists in the neuromotor system that subsequently leads to variability in motor output. This leads to systematic relations in limb trajectory variability at different stages of the movement that are altered when trajectories are modified during movement execution. Hence, by examining the variability in limb trajectories and correlations of kinematic variables throughout movement for vision and no vision conditions, the contribution of visual feedback in the planning and control of movement can be determined.

Hand deviations toward distractors : Evidence for response competition

Abstract It has been suggested that, when movements are planned within cluttered environments, competing responses programmed to distracting stimuli are inhibited based on their relation to the action being performed. Further, as a result of this inhibition, the path of the movement made to the target object deviates away from the distractor. In contrast to the object avoidance hypothesis, the results of the present study show that, for aiming movements made in environments in which distractors are present, the path of the movement veers toward the distractor. Moreover, the effects of the distractors on the movement trajectory were independent of the direction of limb movement. These findings suggest that, when a distractor is not a potential physical barrier, a response to the distractor may be activated along with the target response and, owing to temporal advantages, cause a deviation of the movement trajectory toward the distractor.

Does Joe influence Fred's action?: Inhibition of return across different nervous systems

Inhibition of return (IOR) refers to the slowing of responses to a target that appears in the same location as a previous event. Many researchers have speculated that IOR arises from inhibitory neural processes that have developed through evolution to facilitate efficient search patterns by biasing the action and/or attention of an individual towards novel locations. Throughout evolution, however, humans conducted searches as individuals as well as members of a group. In this context, we sought to determine if IOR could also be observed in the behavior of one individual after the observation of anothers behavior. Consistent with our reasoning, there was no difference in the magnitude of the IOR effect found when participants followed their own response or the response of their partner. These results are discussed in the context of action-based attention and possible underlying neural mechanisms.

Cerebral specialization and the control of oral and limb movements for individuals with Down's syndrome.

In this paper we review existing research on cerebral specialization in Downs syndrome (DS) individuals, and we present a preliminary model. The model proposes that the cerebral organization of DS persons is such that there is a dissociation of brain areas responsible for speech perception and the production of complex movement including speech. Research is presented that confirms some initial predictions of the model.

Salience of stimulus and response features in choice-reaction tasks

A pattern of differential reaction time (RT) benefits obtained in spatial-precuing tasks has been attributed to translation processes that operate on mental codes formed to represent the-stimulus and response sets. According to the salient-features coding principle, the codes are based on the salient stimulus and response features, with RTs being fastest when the two sets of features correspond. Three experiments are reported in which the stimulus and response sets were manipulated using Gestalt grouping principles. In the first two experiments, stimuli and responses were grouped according to spatial proximity, whereas in the last experiment, they were grouped according to similarity. With both types of manipulations, the grouping of the stimulus set systematically affected the pattern of precuingbenefits. Thus, in these experiments, the organization of the stimulus set was the primary determinant of the features selected for coding the stimulus and response sets in the translation process.

Stimulus–Response Compatibility for Vertically Oriented Stimuli and Horizontally Oriented Responses: Evidence for Spatial Coding

It has previously been shown that, when stimuli positioned above or below a central fixation point (“up” and “down” stimuli) are assigned to left and right responses, the stimulus–response mapping up-left/down-right is more compatible than the mapping up-right/down-left for responses executed by the left hand in the left hemispace, but this relation is reversed for responses executed by the right hand in the right hemispace. In Experiment 1, each hand responded at locations in both hemispaces to dissociate the influence of hand identity from response location, and response location was found to be the determinant of relative compatibility. In Experiment 2 responses were made at the sagittal midline, and an inactive response switch was placed to the left or right to induce coding of the active switch as right or left, respectively. This manipulation of relative location had an effect similar to, although of lesser magnitude than, that produced by physically changing location of the response switch in Experiment 1. It is argued that these results are counter to predictions of a movement-preference account and consistent with the view that spatial coding underlies compatibility effects for orthogonally oriented stimulus and response sets.

Visual influences on speech perception in children with autism

The bimodal perception of speech sounds was examined in children with autism as compared to mental age—matched typically developing (TD) children. A computer task was employed wherein only the mouth region of the face was displayed and children reported what they heard or saw when presented with consonant-vowel sounds in unimodal auditory condition, unimodal visual condition, and a bimodal condition. Children with autism showed less visual influence and more auditory influence on their bimodal speech perception as compared to their TD peers, largely due to significantly worse performance in the unimodal visual condition (lip reading). Children with autism may not benefit to the same extent as TD children from visual cues such as lip reading that typically support the processing of speech sounds. The disadvantage in lip reading may be detrimental when auditory input is degraded, for example in school settings, whereby speakers are communicating in frequently noisy environments.

Within- and between-nervous-system inhibition of return: Observation is as good as performance

Inhibition of return (IOR) has been shown to occur when an individual returns to a target location (within-person IOR) and when an individual moves to a location just engaged by another individual (between-person IOR). Although within- and between-person IOR likely result from the same inhibitory mechanisms, different processes must activate these mechanisms following the performance and observation of action. Consistent with the suggestion that the mirror neuron system may be responsible for activating the inhibitory mechanisms behind IOR on observation trials, between-person IOR was only detected under restricted viewing conditions known to activate mirror neurons. These results indicate that mirror neuron system may be involved in both higher-order and automatic cognitive behavior.

Manual and oral praxis in adults with Down's syndrome

Mentally handicapped adults with and without Downs syndrome performed single movements and movement sequences following both verbal and demonstration cueing conditions. While the type of cue did not influence the performance of control subjects, Downs syndrome individuals exhibited more error following verbal cueing. These findings could not be explained on the basis of verbal encoding differences between the groups. The results support the notion that Downs syndrome persons suffer from a dissociation of the functional system responsible for speech perception and the system involved with the organization of complex movement.