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In recent years, the links between neural activity and perception have been an area of interest in cognitive neuroscience. Combined psychophysiological and psychophysical experiments provide a new powerful tool for establishing the relationship between neural activity and perceptual performance. In animals, intracellular recordings combined with psychophysical detection indices have revealed that a particular neuron or set of neurons can play a critical role in the generation of a perceptual event, showing detection functions (referred to as neurometric functions) which are remarkably similar to psychophysical detection functions, or psychometric functions (Parker & Newsome, (1998) Annu. Rev. Neurosci. , 21, 227-277). As noninvasive techniques for recording neural activity are now available, studies combining neuroelectric and psychophysical measures in humans are sparse. In the present study, the accuracy of the human brain in detecting differences in sound duration and the subject's ability to perceive the same differences were tested by means of mismatch negativity (MMN) and the distance between the distributions of false alarms and hits (sensitivity index d'), respectively. It was found that the accuracy of the human auditory system to represent sound duration information is related to the duration context in which the sounds are heard, and that these contextual representations determine the accuracy of perception at the behavioural level.

The possibility that the visual system is able to register unattended changes is still debated in the literature. However, it is difficult to understand how a sensory system becomes aware of unexpected salient changes in the environment if attention is required for detecting them. The ability to automatically detect unusual changes in the sensory environment is an adaptive function which has been confirmed in other sensory modalities (i.e. audition). This deviance detector mechanism has proven to be based on a preattentive nonrefractory memory-comparison process. To investigate whether such automatic change detection mechanism exists in the human visual system, we recorded event-related potentials to sudden changes in a biologically important feature, motion direction. Unattended sinusoidal gratings varying in motion direction in the peripheral field were presented while subjects performed a central task with two levels of difficulty. We found a larger negative displacement in the electrophysiological response elicited by less frequent stimuli (deviant) at posterior scalp locations. Within the latency range of the visual evoked component N2, this differential response was elicited independently of the direction of motion and processing load. Moreover, the results showed that the negativity elicited by deviants was not related to a differential refractory state between the electrophysiological responses to frequent and infrequent directions of motion, and that it was restricted to scalp locations related to motion processing areas. The present results suggest that a change-detection mechanism sensitive to unattended changes in motion direction may exist in the human visual system.

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The first aim of this study was to explore the relation between cognitive reserve, age, and neuropsychological functioning in a healthy sample; and second, to determine the risk of showing cognitive deficits as a function of cognitive reserve. One hundred forty-six healthy participants between the ages of 20 and 79 were submitted to neuropsychological assessment, focusing on attention, memory, visuo-construction, conceptualization and reasoning. Premorbid IQ as measured with the Wechsler Adult Intelligence Scale Vocabulary subtest was used as a proxy of cognitive reserve. Multivariate regression analysis with age and premorbid IQ as explanatory factors revealed a significant effect in all neuropsychological tests. Logistic regression revealed that participants with low cognitive reserve were more likely to obtain deficient scores (< or =1.5 SD below the mean) in the cognitive domains of attention (odds ratio [OR], 3.13; 95% confidence interval [CI], 1.059.29), memory (OR, 6.17; 95% CI, 1.69-22.61) and global functioning (OR, 6.44; 95% CI, 2.56-16.22) than participants with high cognitive reserve. Results suggest that cognitive reserve acts as a protective factor against the expression of cognitive decline related to age in healthy individuals.

Event-related potentials (ERPs) were recorded from healthy young and older subjects during the execution of a visual search task in which they were required to detect the presence of a target stimulus that differed from distractors in a salient feature (orientation). Apart from the orientation target, a task-irrelevant singleton defined by a different feature (color) was also presented without instruction. The effects of normal aging on the N2pc component, an electrophysiological correlate of the allocation of visuospatial attention, were evaluated for the first time. Behavioral results showed an increase in the mean reaction time (RT) and a reduction in the hit rates with age. Electrophysiological results showed a consistent N2pc for orientation target pop-outs but not for irrelevant color pop-outs in both age groups, suggesting that the irrelevant color singleton did not induce attentional capture. Furthermore, the N2pc component observed for orientation targets was significantly delayed and attenuated in older subjects compared to young subjects, suggesting a specific impairment of the allocation of visuospatial attention with advancing age.

These results suggest that the automatic attraction of attention by a peripheral cue results in improved sensory processing at the cued location. This facilitation is replaced by an inhibitory effect when SOA increases, although cue informativeness may modulate this effect. Central cueing does not affect sensory processing at the P1 level.

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