Neural Processing to Visual Stimuli in a Three-Choice Reaction-Time Task

Some authors have suggested that certain components of the event-related potentials (ERPs) reflect underlying stages in the discrimination process. Previous studies have shown that in an auditive three-choice reaction-time task the discrimination is accomplished as a two-stage process, with the more frequently occurring stimulus discriminated at an earlier point than the rarer stimulus and the subjects could be classified as fast and slow responders in function of their response to the most frequent of the three tones. We continuously recorded the electrocerebral activity (EEG) from the scalp and the electromyographic activity (EMG) from the responding muscles in a visual three-choice reaction-time task in 10 strictly right-handed subjects. EEG and EMG responses were subsequently analyzed off-line by aligning them by the onset of either the stimulus (stimulus-synchronized) or the response (response-synchronized). The results suggest that processes of visual stimuli evaluation and response execution are continuously integrated. The discrimination and response systems to visual stimuli is accomplished as a three-stage process, one to frequent tone, another for rare 1, and the last for rare 2. The subjects were classified as fast and slow responders in function of their response to the most frequent of the three tones.     

Visual dreams in the congenitally blind?

An EEG study of sleep in congenitally blind persons revealed a significant correlation between the visual activity reported during dreaming and the decrease of alpha strength recorded from the central and occipital regions of the scalp. This provides the first objective evidence that subjects who have never had visual experiences can have dreams with virtual images that are probably mediated by the activation of the cortical areas responsible for visual representations.     

Effects of long-term blindness on preparatory emg modulation in humans performing landing movements

To investigate the long-term effect of blindness on the task of leaping down to a lower landing surface, five blind individuals were compared with 10 sighted individuals who performed landing movements with and without sight. Participants performed six consecutive drop-landings from four different heights, during which the prelanding modulation of EMG timing and amplitude in four lower-limb muscles were recorded. Analysis showed that blind individuals showed specific prelanding EMG modulation, suggesting that long-term dependence on somesthetic and vestibular cues leads to different preparatory measures for vertical falls.     

Making the uncontrollable seem controllable: the role of action in the illusion of control

It is well known that certain variables can bias judgements about the perceived contingency between an action and an outcome, making them depart from the normative predictions. For instance, previous studies have proven that the activity level or probability of responding, P(R), is a crucial variable that can affect these judgements in objectively noncontingent situations. A possible account for the P(R) effect is based on the differential exposure to actual contingencies during the training phase, which is in turn presumably produced by individual differences in participants' P(R). The current two experiments replicate the P(R) effect in a free-response paradigm, and show that participants' judgements are better predicted by P(R) than by the actual contingency to which they expose themselves. Besides, both experiments converge with previous empirical data, showing a persistent bias that does not vanish as training proceeds. These findings contrast with the preasymptotic and transitory effect predicted by several theoretical models.     

Le geste approprié au juste moment : faut-il une horloge pour que le mouvement soit dans les temps ?

The movement of a body is defined as a variation of its position in time (dx/dt). However, referring to time to describe a movement does not imply that the production of a biological movement necessitates an explicit control of the temporal parameters, and even less that such a control has to be performed with the help of a clock. In this review of the literature, we will try to show, through an analysis of the protocols used, that the answer to this question critically depends on the motor task to be performed. Possible directions towards a convergence will be proposed.     

The relation of white matter hyperintensities to cognitive performance in the normal old: education matters

This study examined whether the severity of cerebral white matter abnormalities (evident on MR images as white matter hyperintensities (WMH)) was related to the cognitive performance of 141 high-functioning older adults. The elderly showed the typical age decrement on measures of processing speed, working memory, and inhibition; however WMH severity was significantly related only to processing speed. The strength of this relationship was, however, influenced by the educational level of the participants, such that processing speed was more associated with WMH severity in less-educated than in well-educated participants. This is consistent with recent concepts of cognitive reserve, but does raise a question as to the underlying source of the cognitive decrement found in the sort of well-educated elders typically used in cognitive-aging studies.     

Evidence of different developmental trajectories for length estimation according to egocentric and allocentric viewpoints in children and adults

This study investigated the influence of egocentric and allocentric viewpoints on a comparison task of length estimation in children and adults. A total of 100 participants ranging in age from 5 years to adulthood were presented with virtual scenes representing a park landscape with two paths, one straight and one serpentine. Scenes were presented either from an egocentric or allocentric viewpoint. Results showed that when the two paths had the same length, participants always overestimated the length of the straight line for allocentric trials, whereas a development from a systematic overestimation in children to an underestimation of the straight line length in adults was found for egocentric trials. We discuss these findings in terms of the influences of both bias-inhibition processes and school acquisitions.     

Aphasic naming in Spanish: predictors and errors

Sixteen Spanish aphasic patients named drawings of objects on three occasions. Multiple regression analyses were carried out on the naming accuracy scores. For the patient group as a whole, naming was affected by visual complexity, object familiarity, age of acquisition, and word frequency. The combination of variables predicted naming accuracy in 15 of the 16 individual patients. Age of acquisition, word frequency, and object familiarity predicted performance in the greatest number of patients, while visual complexity, imageability, animacy, and length all affected performance in at least two patients. High proportions of semantic and phonological errors to particular objects were associated with objects having early learned names while high proportions of no-response errors were associated with low familiarity and low visual complexity. It is suggested that visual complexity and object familiarity affect the ease of object recognition while word frequency affects name retrieval. Age of acquisition may affect both stages, accounting for its influence in patients with a range of different patterns of disorder.