Publications of Czigler, I.

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.

Event-related potentials and the identification of deviant visual-stimuli

The effects of deviant visual stimuli on event-related potentials were investigated in a counting task (Experiment 1) and in a reaction time task (Experiment 2). In Experiment 2 the interstimulus interval was either short or long (340 vs. 1020 ms). The stimuli (two angles within a frame) were frequent (Standard) or deviant (differing from the Standard either in the orientation of the two angles, or in the thickness of the frame, or in both of these features). In various conditions the target stimuli were defined by one of the deviant features or by the conjunction of these features. Subjects were more accurate in the counting task, and the reaction time was shortest when the target feature was the deviant angle orientation. Performance was lowest for the conjunction of the deviant features. The deviant angle orientation elicited a posterior negative wave in the 140-180 ms range. As the interstimulus interval increased, the magnitude of this component decreased. All stimuli with relevant (attended) deviant features elicited another posterior negative wave in the 180-260 ms range as well as an anterior positivity with similar latency. When the interstimulus interval was short, and the only target was the Conjunction Deviant, the summed occipital activity to the relevant features of deviant nontarget stimuli was larger than the negativity to the Conjunction Deviant. Target stimuli elicited late positive waves, which were sometimes preceded by central negativity.

Age and inter-stimulus interval effects on event-related potentials to frequent and infrequent auditory stimuli

The aim of this study was to investigate aging effects on non-attended changes of auditory stimulation, by using psychophysiological methods. Event-related potentials (ERPs) were recorded to frequent (standard; 950 Hz, p = 0.9) and infrequent (deviant; 1045 Hz, p = 0. 1) auditory stimuli in older (mean age = 60.8 years) and younger (mean age = 21.3 years) subjects. In various blocks the inter-stimulus interval (ISI) was either 800, 2400 or 7200 ms. During the experimental sessions the subjects read books, and ignored the auditory stimuli. As a function of ISI, the amplitude of the NI and the amplitude and latency of the P2 increased. The P2 amplitude was larger in the younger group. In the 120-180 ms latency range the deviant stimuli elicited more negative ERPs (mismatch negativity, MMN) than the standard stimuli. The amplitude of the MMN did not change as a function of ISI. MMN was larger in the younger group. Thus the younger subjects were more sensitive to the deviant stimuli. In the younger group, at the two shorter ISIs, the MMN was followed by a positive wave (P3a). The emergence of this component is an indication of the increased activity of the orienting system in the younger subjects, in comparison to the older age group.

Event-related potentials to irrelevant deviant motion of visual shapes

Event-related potentials to visual shapes moving across the visual field were recorded from 10 subjects. The subjects had to respond to the appearance of one of the shapes, while other shapes were irrelevant. On the periphery some of the shapes changed their orientation or their form. Sometimes the direction of movement was different from the standard direction. Subjects did not detect the changes of the pattern on the visual periphery, and the ERPs to these non-detected deviants were identical to the ERPs to the standard stimuli. Six subjects detected the irrelevant direction of movement. In these subjects the deviant direction of motion elicited a fronto-central positive wave (P3s) with 322 ms mean latency. There was no such sharp positive peak in the four subjects who did not detect the deviant direction of movement. Unlike the non-target stimuli. the targets elicited a large positive wave (P3b) with 530 ms mean latency.

Event-related potentials in a lexical stroop task

In a reaction time (RT) situation the subjects made word/non-word decisions to strings of four letters. The original strings could be either words or non-words when read from left to right. Decisions were made for strings resulting when reading the letters in a different sequence specified on each trial. The 'non-word' RT was longer than the 'word' RT, and RT increased further when the (correct) non-word decision was made to strings which constituted a word in the (traditional) left to right order. Event related potentials (ERPs) following the strings were more negative on the left side (the onset of the negativity was approx. 240 ms). Motor reactions were preceded by an epoch (700-300 ms before the response) where the ERPs of trials with stimulus/response conflict were relatively positive. However, the negativity preceding the response (motor potential) appeared to be independent of the stimulus/ response conflict. 'Word' responses were preceded and followed by a positive wave, independent of the motor potential. This positivity is considered to be a very late member of the P3 complex related to lexical memory processes.

Event-related potentials in a visual-discrimination task – negative waves related to detection and attention

Event-related potential effects of deviant stimuli were investigated in a visual discrimination task. The stimuli (two angles within a frame) were either frequent (Standard) or one of two types of infrequent deviant (Deviant 1 or Deviant 2) stimuli. In comparison to the Standard stimuli, for Deviant 1 the two angles differed in their orientation, whereas for Deviant 2 the angles were identical but the frame was thicker. In Condition 1 the subjects counted the number of Deviant 1 stimuli. Of the 13 subjects, 12 did not detect the fact that some of the frames were thicker in this condition (i.e., for the Deviant 2 stimuli in Condition 2). The task in Condition 2 was the same (i.e., the target was Deviant 1), but the subjects were instructed about the thicker frame of Deviant 2 stimuli. In Condition 3, Deviant 2 stimuli became the targets. In comparison to the Standard, Deviant 1 elicited two posterior negative waves in the 120-180 and 240-300 ms latency ranges respectively. In addition, when Deviant 1 was the target stimulus (Conditions 1 and 2), this stimulus elicited the N2 and the P300 as well. In contrast, the irrelevant Deviant 2 elicited no such waves. In the target position (Condition 3), Deviant 2 elicited the second posterior negativity, the N2, and the late positivity. The earlier negativity is considered to be a correlate of processes connected to the automatic detection of the deviant features, whereas the later negativity is considered to be related to attentive processes, i.e., this wave is considered to be a member of the family of processing negativities.