Psychophysiology, cognitive neuropsychology and neuroscience

[6 abstracts]

1. Neural correlates of visual search and change blindness: An fMRI study  
Kaplar M., Deak A., Toth L., Bognar P., Bernath L.
First author's affiliation: University of Pecs, Pecs, Hungary

The phenomenon "change blindness" means that people can not recognize changes between two or more stimuli, if there is a masking stimulus between the two others. This phenomenon gives us the opportunity to use change blindness in experiments examining attention. In a change blindness task the subjects have to recognize the difference between two similar pictures with a masking screen between them. This task can be used to map unconscious attention and the processing of unconscious information because the target (what? and where?) is unknown by the subject. In our experiment we examined if a conscious attentional task like visual search activates the same brain areas as solving a change blindness task. In an fMRI study we presented two very similar sets of stimuli, one for visual search, one for change blindness task. We used the activations during the a visual search task as baseline in the analysis of activations during the change blindness task. We got few activated brain areas like Middle Occipital and Temporal Gyrus, Fusiform Gyrus, Supramarginal Gyrus, Nucleus Caudatus and Thalamus due to performance. The activation of these areas can be explained well by the differences of a the two types (search vs. recognize, conscious vs. unconscious) of the two tasks used in the study.

2. Repressors show more prefrontal brain activity to irrelevant negative stimuli during a visual search task: An fMRI preliminary study  
Deak A., Kaplar M., Toth L., Bogner P., Revesz G., Bernath L.
First author's affiliation: University of Pecs, Institute of Psychology, Pecs, Hungary

People with repressive personality style tend to keep distance from threatening or negative emotional experiences. When faced with unpleasant stimuli, they show higher level of responsiveness due to physiological mechanisms. They have been found hypersensitive in their cognitive attention. In our fMRI study, we investigated repressor and non-repressor subjects' brain activity during a visual search task. Using a block-design paradigm, subjects were instructed to follow numbers in a matrix while either an unpleasant (active phase) or a neutral picture (baseline phase) was presented in the background. Our preliminary results show that repressors have more neural activation in the right prefrontal cortex (superior frontal gyrus, medial frontal gyrus) and left inferior temporal gyrus. Activation in the cingular cortex have been found in the non-repressor group.

3. Influence of interhemispheric differences on the Stroop and the Reverse Stroop effect  
Nikolić M., Juranić I.
First author's affiliation: University of Zadar, Zadar, Croatia

The Stroop effect is demonstration of interference in the reaction time of a task, where subjects have to ignore the word’s semantic meaning and react on the word’s color. Opposite effect is the reverse Stroop effect where subjects have to react on the word’s semantic meaning and ignore the word’s color where extension of reaction time is also obvious. Methods; One of the possible explanation are interhemispheric differences in elaboration of information - so the aim of this study was to explore effects of interhemispheric differences on the Stroop and the reverse Stroop task in groups of extreme left handed (N = 10) and extreme right handed (N = 10) subjects. The subjects were asked to solve two kinds of tasks, Stroop (naming color) and reverse Stroop (reading word), within different conditions (neutral, congruent and incongruent for the Stroop task and congruent and incongruent for the reverse Stroop task). In every situation they reacted with right and left hand. In right handed group both effects were identified while in left handed group only Stroop effect occurred. Subjects from both groups made more mistakes in incongruent conditions of both tasks, because of interference which is caused with difference in semantic meaning and ink color of the word. Interesting finding is that in right handed group Stroop effect is larger when subjects were reacting with right hand and reverse Stroop effect when reacting with left hand. This is the result of difference in interhemispheric elaboration of information where left hemisphere is dominant for verbal information and right hemisphere for color information. This has not been identified in left handed group because left handed individuals have more fibers in corpus callosum, which ensures better interhemispheric interaction and reduces interference.

4. Stable and state-dependent impulsivity in bipolar disorder   [presentation, ppt, 949 kB]
Milavec M., Šprah L.
First author's affiliation: Sociomedical Institute at SRC SASA, Ljubljana, Slovenia

One of prominent and measurable characteristic of Bipolar disorder is impulsivity which may have both stable and state-dependent aspects. Emotional modulation of cognitive control, which is state-depended aspect of impulsivity, has been reported as attentional bias to positive and negative information. The present study aimed to determine whether emotional valence of stimulus influences cognitive control in bipolar patients compared to healthy individuals and whether there is an interaction between stable and state-dependent aspect of impulsivity in bipolar disorder. We compared 39 bipolar outpatients and 38 healthy individuals, matched for age, gender and years of education. All participants completed Baratt Impulsiveness Scale 11 (BIS-11) and computer administered Affective Go/No-Go Task (including pictures of negative, positive and neutral emotional valence taken from International Affective Picture System). On Affective Go/No-Go Task bipolar outpatients demonstrated longer reaction times to emotional stimuli and more errors on global score in compare to the control group, especially in negative and neutral contexts and when the targets were pictures with neutral emotional valence. Global score on BIS-11 indicated that bipolar outpatients had higher levels of trait impulsivity than healthy individuals. Bipolar patients with heightened levels of trait impulsivity also underestimated stimuli with positive emotional valence and tended towards underestimation of stimuli with negative emotional valence. These data suggest that patients with bipolar disorder have poorer control of cognitive inhibition than healthy subjects, probable due to increased levels of impulsivity and other associated cognitive impairments. We confirmed that emotional valence of stimulus influences cognitive control in bipolar patients compared to healthy subjects and that there is an interaction between stable and state-dependent aspect of impulsivity in bipolar disorder.

5. Subjects' effort in Fitts Tapping Tasks regarding the task difficulty  
Brecic A., Manenica I.
First author's affiliation: Department of Psychology, University of Mostar, Mostar, BIH

Fitts tapping task (FTT) consists of 12 psychomotor tasks, which difficulty varies from one to six bits. Previous studies where FTT was used, showed a linear decrement in performance and also a linear increment in the task difficulty assessment as the task difficulty objectively increased. Since the tasks consist of motor and mental components, this would mean that the motor component decreases and the mental component increases as the task difficulty increases. In the view of this, it could be argued that summative effort (motor plus mental) which subjects put in the task remains the same throughout the tasks. The aim of this study was to check this hypothesis by using different heart rate parameters as indicators of the total effort put in the task by the subject. If this effort were constant, the cardiac indices would not significantly differ throughout the tasks. Fifteen subjects performed all the tasks for five minutes each, while their cardiac R-R intervals were continuously recorded before, during and after the task. Their performance (number of target hits) was also recorded, together with intertap intervals. At the completion of every task subjects were asked to assess their difficulty on Borg's scale. As expected, the results showed a fall in the number of target hits as the task difficulty increased, and an increase in the task difficulty assessment. The analysis of cardiac R-R intervals included classical analyses, as well as spectral analysis procedure. All the parameters showed differences between the preceding resting and the five-minute working periods. There was no difference, however, amongst the tasks of various difficulties. The results suggest, although the load contents of the tasks change as their difficulty changes, the total effort, put in the task by subjects, remains the same regardless of the task difficulty.

6. Differentiation of motor and cognitive load components in Fitts tapping tasks  
Manenica I., Šuto A.
First author's affiliation: University of Zadar, Zadar, Croatia

The aim of this study was to try to differentiate relative contributions of motor and cognitive load components in Fitts tapping tasks (FTT) by keeping the motor component constant throughout the tasks in one situation, and comparing it with parameters in the standard situation. Twelve subjects performed the series of FTT in the standard way and in the situation with constant motor load, identical to the individual speed in the most difficult standard task. The working time for every task was five minutes. In both situations, target hits, intertap times and subjects' cardiac R-R intervals were continuously recorded. At the completion of each task subjects estimated its difficulty on Borg's scale (Borg, 1973). Performance indices (number of target hits and intertap time) changed as expected in relation to the task difficulty and the differences between the two experimental situations. Parameters and spectral analyses of R-R intervals in the middle frequency range (0.7- 0.14 Hz) showed differences in and between the two experimental situations, indicating a decrease in motor and an increase in mental component, as well as a higher overall task load in the standard situation due to a greater motor involvement. The task difficulty assessment on Borg's scale showed almost linear increase with the task difficulty, as well as a difference between the two experimental situations, indicating significantly lower task load in the situation with constant motor load. On the basis of regression lines between the task difficulty (bits) and the scale assessments in the two situations (y = 0.7+2.228x and y = -1.55+2.37x), the assessments in both situations were transformed into the difficulty equivalents in bits. The difference between the lines was equivalent to 0.71 bits, which was attributed to the differences in the motor involvement. These results showed, generally speaking, cognitive component in FTT as more prominent in task load than motor component.