Publications of Ambro, A.

Aging, stimulus identification and the effect of probability: An event-related potential study

Event-related potentials (ERPs) of younger and older subjects were compared in a simple reaction time (SRT) and in two GoNogo (20% and 80% target probability) tasks. At the T5 location, the NA component (the difference between the ERPs elicited by the frequent stimuli in the GoNogo tasks on the one hand, and the ERPs in the SRT task on the other hand) emerged earlier in the younger group. The N2b was larger in the younger group, and in this group the rare stimuli of the 80% GoNogo task elicited an enlarged N2. When compared to the older group, the stimulus probability in the younger group had a larger effect on the amplitude of the late positivity. The results show age-related changes at an early stage of the information processing activity, and larger sensitivity of the orienting system in the younger subjects.

Effects of stimulus alternation, repetition and response requirements on event-related potentials to patterned visual stimuli

Event-related potentials (ERPs) were recorded to square-pattern stimuli presented either to the upper or the lower half of the visual field. in the Same task the subjects had to respond to the fifth stimulus of a microsequence of stimuli that appeared on the same half field, whereas in the Different task the target stimulus was the alternation of stimulus location after a microsequence of four stimuli to the same half field. The pattern-specific CII component (a negative wave to lower half-field stimulation with 100 ms latency) appeared to be insensitive to task variables. N1 increased to the uncertain alternations of stimulus location. An N2 component with temporal maximum emerged to Nogo stimuli (to the fifth stimulus in the same location in the Different task and the alternation after four identical stimuli in the Same task). An anterior N2 was characteristic to the Nogo stimuli of the Different task. P3 latency was longer, and it had more anterior distribution to the Nogo stimuli.

Event-related potentials and aging – identification of deviant visual-stimuli

The effects of aging on event-related potentials (ERPs) were investigated in visual tasks. The stimuli (two angles within a frame) were frequent (standard) or deviant (differing from the standard either in the orientation of the two angles, in the thickness of the frame, or in both). The target stimuli were defined either by the presence of only one deviant feature, or by the conjunction of the deviant features. The deviant stimuli elicited an increased P2, a posterior N2, on N2b, and a tate positivity (Go and Nogo P3). The latencies of all but the P2 were longer in the older subjects. In the younger group, the target stimuli elicited a larger late positivity than the non-target stimuli that had deviant features, whereas in the older group the target stimuli did not elicit a larger P3 than the stimuli with two deviant features, even when this deviant was a non-target. In contrast to the younger group, in the older group we obtained no P3 over the temporal and occipital locations. We found a reduction of P3 over the posterior location even in a group of middle-aged (mean age = 39 years) subjects. In tasks with only one target feature, the false alarm rate was higher in the elderly subjects. These results suggest a gradual age-related slowing down of the attentive processing of deviant visual patterns, and a decrease of inhibitory functions in the elderly group.