Hemispheric asymmetry in event related potentials associated with positive and negative emotions.

Event-related potentials from symmetrical points of the left and right frontal and occipital cortex were recorded while subjects experienced positive and negative emotions. The emotions were elicited by either missing or hitting a target with a photoelectric gun. Twenty three right-handers (10 males and 13 females) were tested. Each subject took part in two sessions. In the first session the subjects were informed about their performance (hit or miss) after each shot. In the second, control session, no feedback was given. The amplitudes of P180 potential registered from the occipital cortex were higher in the right than in the left cerebral hemisphere, irrespectively of subjects' performance (i.e. a miss or a hit). No such tendency was observed in potentials registered from the frontal cortex. These regularities emerged only in the feedback situation, i.e. when subjects were informed about their performance, although higher ERPs were registered for hits than for misses. The results support the hypothesis that the posterior region of the right hemisphere is more engaged than the left one in experiencing emotions, irrespectively of their sign.

Hemispheric differences in evoked potentials to pictures of faces in the left and right visual fields.

Fifteen right-handed women evaluated the similarity of two faces presented to them either in the left or in the right visual field. The subjects' task was to decide whether the faces were the same or different and accordingly to press a button or abstain from doing so. Errors made by the subjects and the visual evoked potentials (VEPs) from points O1 and O2 referred to point CZ were recorded. Behavioural and electrophysiological results demonstrated the superiority of the right hemisphere in the perception of faces. The subjects made fewer errors when faces were presented in the left visual field. The number of errors also decreased when the presented faces were different from each other. Analysis of the VEPs indicates the existence of hemispheric asymmetry as early as 100 msec after the first stimulus disappeared. The asymmetry is larger in response to the second stimulus. On the basis of these results we conclude that differentiation in hemispheric functions takes place in the phase of short-term memory. The smaller number of errors made when the presented faces were different we explain by the strategy applied by the subjects.

Cerebral hemispheric differences in visual perception of various types of verbal material.

Hemispheric differences in perception of various verbal material were sought in two groups of Ss: 10 normal adults (a control group) and 10 patients of the Neurosurgery Clinic with focal brain damage either to the left or right hemisphere. The stimuli were letters projected singly, in three-letter nonsense sequences or in three letter Polish words on a screen in the left or right visual half-field. The results obtained from the control groups indicate that the dominance of the left hemisphere is limited only to the meaningful verbal material. The results obtained from the patients support the first finding and show that this dominance can be cancelled by some left hemisphere damage without influence on the perception of meaningless material.

Evoked response correlates of letter recognition.

The positive late wave of the average evoked responses induced by tachistoscopic presentation of single letters had a higher amplitude when the letters were correctly recognized than when they were not. The results suggest that the late positive component of VER is a correlate of complex cognitive processes engaged in object’s identification.

Search for structures involved in integration of letters in pairs.

Two experiments aimed at finding, at what stage of perceptual processing the positive interactions between letters, observed in some previous studies, are established. Single letters and pairs of letters were exposed. The task of the subjects was to recognize letters. In Experiment I bright letters on a black background were used instead of black letters on bright background used in previous experiments. Such change of brightness within the stimuli did not influence the character of interactions between letters. This suggests that the positive interactions are connected with higher level of visual system. In Experiment II patients with damage of various areas of the brain cortex were tested. The facilitation between two letters did not occur in patients with prestriate lesions, although it can be observed in patients with different localization of lesions. This suggests that prestriate cortex is involved in positive interactions between letters.

Interactions between two spatially separated letters presented in succession.

The interactions between two letters presented in succession to neighboring regions of retina were investigated. The interstimulus intervals were: 0, 20, 60, 250 ms, 2.5 s. In control trials single letters were presented in two positions corresponding to the positions of letters in pairs. The recognition of a letter presented as the first element of pairs with either simultaneous presentation or with 250 ms delay of the second element was significantly better than the recognition of single letters. On the contrary, the interstimulus interval 20 and 60 ms yielded an increase of errors made in the recognition of the first letter. The results are interpreted in terms of inhibitory interactions between transient and sustained channels, and in terms of hypothesized excitatory connections between the cortical cells responding to visual elements forming more complex patterns.

The effect of distractor on memory for pitch: trace distortion or interference with retrieval?

The effect of the time of presentation of an interpolated stimulus on dynamic memory for pitch of pure tones of 900-2000 Hz was investigated by comparison of successive stimuli. The test tone followed the sample tone after 25, 40, 60, 80, 160 or 320 s. The interpolated stimulus (a pure tone of 220 Hz) was timed either 20 s before the test tone (Experiment I) or 20 s after the sample (Experiment II). The effect of the interpolated stimulus on memory for pitch was found to vary with the time interval between this stimulus and the test tone. An interfering effect was observed when this interval did not exceed 40 s. No variation in effect occurred within this time limit. These findings suggest that the distracting stimulus interferes with the retrieval of the memory trace of the sample tone rather than with the trace itself.

Specific visual disability in relation to ontogeny of brain asymmetry.

Children with retarded development of visual perception were compared with previously tested normal children Verbal and non-verbal patterns were presented either to the left or to the right hemisphere. In both groups of children the results showed a functional equality of the hemispheres during analysis of the non-verbal patterns. Left hemisphere superiority for verbal material in Normal group was not confirmed by the results in Retarded children. The data are discussed in terms of the relation between the ontogeny of brain asymmetry and specific visual disability in children.

Hemispheric differences in the visual analysis of the verbal and non-verbal material in children.

Five years old children, who could not read, and the same children at the aged of 7, who already knew letters, were used as subjects. A visual procedure involved presentation of single letters or a pair of letters randomly to the left or right of a central fixation point. Reaction time and number of correct identifications, showed by pressing a key, were indicators of the perception of letters. The children of five identified the letters with equal correctness, whether they were addressed to the right or to the left hemisphere, whereas the children of seven showed left hemisphere superiority.

Interaction between two letters in visual perception.

Letters were exposed by tachistoscope for 17 ms to adult subjects. In Experiment I, single letters were exposed. The proportion of errors differed strongly for particular letters. In Experiment II pairs of letters were exposed. The first letter of a pair was recognized more easily than when exposed alone in Experiment I. In Experiment III pairs of letters were exposed but the subject's task was to recognize only one letter of the pair. Both, first and second letters of the pair were then recognized better than in Experiment I. The results were interpreted in terms of facilitatory and inhibitory effects occurring on different levels of the visual system.

Interactions between two simple visual patterns.

The interaction of linear and dot elements of simple visual patterns was examined. The following patterns were used: short line-dot, long line-dot, right turned angle-dot, downward angle-dot, circle-dot, and two dots. Except for circle-dot and two dots, perception of either of both elements of the composite stimulus deteriorates as compared to perception of the same elements when presented separately. Perception of either element is improved in the case of the circle-dot stimulus, while in the case of two dots the number of errors remained at approximately the same level. It is hypothesized that both susceptibility to influence from the other element in a composite stimulus and intensity of masking effect produced by the given stimulus depend on distance between the information points of masking and masked stimuli. The extent of susceptibility is also connected with perceptual difficulty in identification of a stimulus when presented separately.

Analysis of perception of complex visual stimulus-patterns.

This paper deals with the analysis of visual perceptions of complex patterns consisting of two simple patterns placed one above the other in one frame (united pattern) or in two separate frames each (divided pattern). The upper pattern consisted of a configuration of lines, the lower one of a configuration of dots. There were one positive pattern which a subject had to recognize in tachistoscopic exposure and a number of negative patterns which a subject had to reject. When the dot component of the positive pattern consisted of two dots situated near its left edge, the subjects committed a great number of errors in recognition of the positive pattern and also the negative patterns with dot-negative components. Errors in recognition of negative patterns with line-negative components were much less numerous. Generally less errors were committed with divided patterns than with united patterns. When in the dot component of the positive pattern the distance between the dots was increased and they were placed symmetrically, the number of errors in recognition of this pattern decreased considerably; errors made in rejecting the negative patterns were, however, the same as in the previous test. Contrary to the previous test, errors with united patterns were less numerous than with divided patterns. The data obtained are discussed with reference to the concept of lateral inhibition between components of the complex unknown patterns. It is postulated that this inhibition can be partially overcome if the components of the complex pattern are easy integrated as is the case with symmetric united patterns.