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Visuo-manual aiming movements in 6- to 10-year-Old children: evidence for an asymmetric and asynchronous development of information processes.

Sixty children from 6 to 10 years old participated in an open-loop visuo-manual aiming task (Experiment 1). They were asked to point as fast and accurately as possible toward lateralized visual targets. Responses were wrist flexion-extension movements. Results showed non-monotonic changes with age of constant error, reaction time, and movement time. Constant error for targets presented in the right visual field increased between 6 and 8 years and decreased afterward. Reaction time and movement time decreased with age except at 8 years where they tended to increase. The same subjects participated in two control tasks. One task was designed to test the spatial localization of the lateralized visual targets (Experiment 2). Results showed that subjects localized very accurately the targets at all ages. The second control task was designed to test simple reaction time to the same visual stimuli used in the previous tasks (Experiment 3). Results indicate that reaction time decreased linearly with age when no spatial processing is required for the production of the response. The results of the three experiments showed different developmental functions according to the processes involved in each task. Moreover, they suggest that the conversion from visual to motor coordinates undergo a qualitative change at 8 years of age, and that the prevailing process of this conversion is located in the left cerebral hemisphere.

Age Factors↗

Does aging affect the allocation of visual attention in global and local information processing?

The earliest studies of Navon (1977) showed that in certain conditions the visual perception of hierarchical stimuli generates a global precedence effect. This hypothesis is based on the joint occurrence of two effects: a response time (RT) advantage for identifying global targets and interference by global distractors when responding to a local target. The aim of the present study was to determine the involvement of attentional mechanisms and whether certain aspects are specifically altered by normal aging. In a selective-attention task, a complete global precedence effect was found for young and old subjects. However, for the old subjects, global interference on local identification was more pronounced than for the young subjects. In a divided-attention task, the RT advantage was affected by attention shifts between global and local forms for both young and old subjects, but the global interference effect did not change.

Adult↗

Measures of information processing in rapid automatized naming (RAN) and their relation to reading.

The letters, numbers, and objects subtests of the Rapid Automatized Naming Tests (RAN) were given to 50 first- and second-grade students. Student performance on the three RAN subtests were audiotaped and subjected to postacquisition processing to distinguish articulation and interarticulation pause times. This study investigated (1) the relations between the articulation and pause durations associated with the 50 stimuli of each RAN subtest and (2) the relations between the pause and articulation latencies of the three RAN subtests and reading. For both first- and second-grade students, pause and articulation times for RAN letters and objects were not found to be reliably related, in contrast to RAN numbers articulation and pause durations. RAN subtest pause durations were differentially related to reading; however, articulation was rarely related to reading. The RAN letters pause time was the most robust predictor of decoding and reading comprehension, consistently predicting all first- and second-grade measures. Analysis supported the view that reading is predicted by speed of processing associated with letters, not general processing speed.

Adolescent↗

An internal current source yields immunity of electrosensory information processing to unusually strong jamming in electric fish.

The electric organ of a fish represents an internal current source, and the largely isopotential nature of the body interior warrants that the current associated with the fish's electric organ discharges (EODs) recruits all electroreceptors on the fish's body surface evenly. Currents associated with the EODs of a neighbor, however, will not penetrate all portions of the fish's body surface equally and will barely affect regions where the neighbor's current flows tangentially to the skin surface. The computational mechanisms of the jamming avoidance response (JAR) in Eigenmannia exploit the uneven effects of a neighbor's EOD current to calculate the correct frequency difference between the two interfering EOD signals even if the amplitude of a neighbor's signal surpasses that of the fish's own signal by orders of magnitude. The particular geometry of the fish's own EOD current thus yields some immunity against the potentially confusing effects of unusually strong interfering EOD currents of neighbors.

Animals↗

Corticofugal modulation of the information processing in the auditory thalamus of the cat.

Single unit activity of 355 cells was recorded in the auditory thalamus of anesthetized cats before, during, and after the inactivation by cooling of the ipsilateral primary auditory cortex (AI). Most of the units (n = 288) showed similar functional characteristics of firing before and after the cryogenic blockade of AI. The spontaneous firing rate remained unchanged by cooling in 20% of the units and decreased in the majority of them (60%). In some regions, i.e. dorsal division of the medial geniculate body (MGB), lateral part of the posterior group of the thalamus, and auditory sector of the reticular nucleus of the thalamus, the maximum firing rate evoked by white noise bursts was generally affected by cooling in the same direction and to the same extent as the spontaneous activity. Units in the ventral division of MGB showed a characteristic increase of signal-to-noise ratio during cortical cooling. The corticofugal modulation led to the appearance or disappearance of the best frequency of tuning in 51 units and changed it by more than 0.5 octave in 34 units. The bandwidths of different response patterns to pure tones stimulation were used to define a set of functional properties. During cryogenic blockade of AI, two cortically modulated sub-populations of units were usually distinguished that exhibited changes for a given functional property. The complexity and diversity of the effects of cortical inactivation suggest that the corticothalamic projection may be the support for selective operations such as an adaptive filtering of the incoming acoustic signal at the thalamic level adjusted as a function of cortical activity.

Acoustic Stimulation↗