Event-related potentials in psychiatry--methodologic principles

The methodological requirements for the use of event-related brain potentials (ERPs) in psychiatry are critically reviewed. In particular the development of psychophysiological models is considered as essential for a functional interpretation of ERP-experiments. In addition problems of signal-analysis and clinical diagnosis relevant to ERP-research in psychiatry are briefly discussed. The logic of ERP-research in psychiatry is illustrated by a series of dichotic listening experiments.     

Event-related potentials and recognition memory

According to dual-process models, recognition memory is supported by distinct retrieval processes known as familiarity and recollection. Important evidence supporting the dual-process framework has come from studies using event-related brain potentials (ERPs). These studies have identified two topographically distinct ERP correlates of recognition memory--the "parietal" and "mid-frontal" old/new effects--that are dissociated by variables that selectively modulate recollection and familiarity, respectively. We evaluate the extent to which ERP data support dual-process models in light of the proposal that recollection is a continuous rather than a discrete memory process. We also examine the claim that the putative ERP index of familiarity is a reflection of implicit rather than explicit memory. We conclude that ERP findings continue to offer strong support for the dual-process perspective.     

Competitiveness in males and in females

Male and female undergraduates performed a task at which they either succeeded or failed in competition with either a male or female partner who subsequently either accepted or rejected them. Subjects who were rejected by a male partner following success or accepted following failure performed less well on a subsequent anagram task than did those who were accepted following success or rejected following failure. These results suggest the importance of situational factors as determinants of fear of success behavior.     

Event-related potentials in phonological matching tasks

Two experiments investigated Event-Related Potentials (ERPs) in matching tasks. In Experiment 1 subjects judged, in separate conditions, whether two words rhymed or were written in the same case. The CNV developing between the two words was larger in the latter task compared to the former at the right temporal site. In the rhyme judgment task, an increased late negativity differentiated the ERPs to nonrhyming words from those that rhymed with the previously presented word. This difference was maximal at the midline and over the right hemisphere. Experiment 2 further investigated ERPs in the rhyme judgment task, increasing memory demands with an extended interstimulus interval (ISI) and varying the number of items subjects had to hold in memory during this period (one vs. three). Irrespective of memory load, CNVs during the ISI were more negative from the left hemisphere, and the ERPs to the rhyming and nonrhyming words showed the same differences as in Experiment 1. The CNV asymmetries are interpreted as being associated with the engagement of lateralized short-term memory processes. The rhyme/nonrhyme differences are possibly related to the “N400” component elicited by semantically incongruous words. Possible reasons for their scalp distribution are discussed.     

Reduced asymmetry in motor skill learning in left-handed compared to right-handed individuals

Hemispheric specialization for motor control influences how individuals perform and adapt to goal-directed movements. In contrast to adaptation, motor skill learning involves a process wherein one learns to synthesize novel movement capabilities in absence of perturbation such that they are performed with greater accuracy, consistency and efficiency. Here, we investigated manual asymmetry in acquisition and retention of a complex motor skill that requires speed and accuracy for optimal performance in right-handed and left-handed individuals. We further determined if degree of handedness influences motor skill learning. Ten right-handed (RH) and 10 left-handed (LH) adults practiced two distinct motor skills with their dominant or nondominant arms during separate sessions two–four weeks apart. Learning was quantified by changes in the speed–accuracy tradeoff function measured at baseline and one-day retention. Manual asymmetry was evident in the RH group but not the LH group. RH group demonstrated significantly greater skill improvement for their dominant-right hand than their nondominant-left hand. In contrast, for the LH group, both dominant and nondominant hands demonstrated comparable learning. Less strongly-LH individuals (lower EHI scores) exhibited more learning of their dominant hand. These results suggest that while hemispheric specialization influences motor skill learning, these effects may be influenced by handedness.     

Event-related brain potentials and human language

The human capacity to produce and comprehend language is one of the most distinctive characteristics of our species. However, understanding the cognitive and neural underpinnings of human language has proved difficult, in part because these processes are rapid, complex and (for the most part) inaccessible to conscious reflection. Methodologies are needed that provide continuous measurement during language processing and that do not rely on a conscious response. One such method involves the recording of event-related brain potentials (ERPs) elicited during language comprehension or production. ERPs are continuous, multidimensional records of the electrical activity that occurs in the brain during the process of interest. We review recent work demonstrating that ERPs are quite sensitive to (at least some of) the psychological and neural events underlying human language. Indeed, researchers have used ERPs to investigate the separability of syntactic and semantic processes, the on-line analysis of sentence constituent structure and the lexical processing capacities of language-disordered populations.     

Sexual fantasizing in males and females

Sexual fantasizing during intercourse, masturbation, and nonsexual activity was examined in 30 males and 30 females, American students at Tel-Aviv University. Each subject responded individually to questionnaires involving general background information, sexual activity, daydreaming frequency and attitudes toward daydreaming, and a sexual fantasy scale. The results indicated that virtually no man or woman denied having sexual fantasies. Any observable sex differences were in kind rather than amount of fantasy. Women had more submission fantasies, whereas men reported more performance fantasies. This difference was interpreted as reflecting social sexual stereotypes. In support of a cognitive skill model, it was found that sexual fantasizing proliferates along with increases in both sexual and daydreaming experience. Sexual passivity was related to a greater degree of fantasizing during sex. On the whole, the findings suggest that sexual fantasizing is a universal occurrence which in itself is not necessarily related to psychopathology.     

Lateral eye-movements and indices of nonanalytic attending in right-handed females.

24 right-handed females were assessed on left-moving after participating in a study wherein they were presented on hypnotic susceptibility and absorption and then attended "nonanalytically" for 20 sessions. Although no significant correlations were found between left-moving and other variables, further analyses indicated a non-linear relationship between left-moving and susceptibility, absorption and self-rated "depth" of attending.     

Fear of success in males and females

Horner's “fear of success” test was administered to 303 children between the 4th and 12th grades. There was an increase of fear of success imagery between the 4th and 10th grades and a decrease between 10th and 12th grades. Fear of success was related to sex only during high school, where it was associated with the course of study pursued by students. Thus, in a high school secretarial course, females showed the lowest fear of success while 12th-grade college-prep females showed fear of success higher than secretarial course females and college-prep males. The findings were interpreted as indicating developmental changes in fear of success due to increasing peer affiliation (4th–10th grades) and sex-linked competitive achievement (high school).     

Event-related potentials in neuropsychological studies of language

Experiments are described in which event-related potentials (ERPs) are employed to study the specialization of functions between and within the cerebral hemispheres during the performance of language and nonlanguage tasks by normal adults. Similar studies of deaf subjects suggest that the functional organization of the brain may be altered after different early language and sensory experiences. Studies of patients with alexia without agraphia suggest that the ERP may be a valuable tool with which to study cerebral reorganization after brain damage.     

Selective activation effects of concurrent verbal and spatial memory loads in left-handed and right-handed adults

Thirty-two left-handed subjects, divided into four groups according to sex and familial sinistrality, and 16 right-handed subjects without familial sinistrality (8 male, 8 female) participated in a tachistoscopic unilateral letter-identification task with concurrent verbal- and spatial-memory loads. Across groups, a significant right visual field advantage for letter-identification was found. In the majority of both left-handed and right-handed subjects, the concurrent verbal-memory load resulted in a selective activation, with the right visual field performance showing improvement. However, the group of left-handed males with a positive family history of sinistrality gave less evidence of selective left-hemispheric activation as a consequence of the verbal-memory load. The concurrent spatial-memory load did not result in a consistent pattern of selective activation.     

Differential predictability of females and males

This study examined the existence of sex differences in validity coefficients from a variety of different types of tests. It was found that female validities significantly exceeded male validities by .04 correlational units. When the validities were broken down by predictor categories, no significant differences were observed between males and females on either personality or high school background measures; and female validities exceeded male validities on tests of abstract reasoning, clerical abilities, information, mathematical abilities, verbal abilities, and composite scores from multiple tests. Implications of these findings are discussed.Use of the Michigan State University computing facilities was made possible through support, in part, from the National Science Foundation.     

Reading between the lines: Event-related brain potentials during natural sentence processing

Event-related potentials (ERPs) were recorded from subjects as they silently read 160 different seven-word sentences, presented one word at a time. Each sentence was in itself a natural, meaningful phrase. Substantial intersubject variability was observed in the ERP waveshapes following the words. More than half of the subjects generated P3 components to word stimuli, but those who did showed similar responses to repeated control presentations of a single word. In addition, it was found that all but the first word in the sentence elicited an ERP with a significant left-greater-than-right asymmetry in the late positivity over temporo-parietal regions. The ERPs to the last words were associated with more late positivity than those to the preceding words. One quarter of the sentences, at random, ended with a word printed in a typeface that was different from that of the preceding words. This infrequent change in typeface elicited a complex ERP having three consistent late positive components.     

Event-related potentials in a two-interval forced-choice detection task

In an attempt to elucidate the nature of the subject’s strategy in a two-interval forcedchoice auditory detection task, event-related potentials were studied at two intensities which yielded mean accuracies of 82% and 98%. Subjects reported the observation interval in which they judged the signal to be present and the confidence of the judgment. Principal components varimax analyses yielded four components: a CZ maximal P300, a Slow Wave, a slow negative shift, and a late negative component. The P300 amplitude findings suggest that different strategies are utilized for high-confidence and low-confidence detections. At high confidence, P300 amplitude is large for the observation interval in which the signal is presented, indicating a strategy involving serial independent detection. However, the P300 latency findings at high confidence suggest that absence of the signal in the first observation interval is nonetheless noted: P300 latency in response to signal presence is shorter for the second observation interval than for the first observation interval. At low confidence, P300 is small or absent for both observation intervals, indicating a deferred decision, presumably arrived at through comparison of the two percepts.     

Event-related potentials to schematic faces in social phobia

Social phobia has been associated with an attentional bias for angry faces. This study aimed at further characterising this attentional bias by investigating reaction times, heart rates, and ERPs while social phobics, spider phobics, and controls identified either the colour or the emotional quality of angry, happy, or neutral schematic faces. The emotional expression of angry faces did not interfere with the processing of their colour in social phobics, and heart rate, N170 amplitude and parietal late positive potentials (LPPs) of these subjects were also no different from those of non-phobic subjects. However, social phobics showed generally larger P1 amplitudes than non-phobic controls with spider phobic subjects in between. No general threat advantage for angry faces was found. All groups identified neutral schematic faces faster and showed larger late positive amplitudes to neutral than to emotional faces. Furthermore, in all groups the N170 was modulated by the emotional quality of faces. This effect was most pronounced in the emotion identification task.     

Event-related brain potentials differentiate normal and disabled readers

Auditory event-related potentials (AERPs) recorded to irrelevant tone pairs while subjects performed visual, reading-related cognitive tasks differed significantly between normal and disabled readers. Disabled readers as compared with normal readers showed significantly lower amplitude right hemisphere AERP responses during tasks that involved visual-phonemic transfer of information and simple pattern recognition. Disabled readers as compared with normal readers also showed significantly higher amplitude left hemisphere responses during the visual-phonemic task. In both experimental conditions the reading-disabled subjects showed significantly lower amplitude right than left hemisphere AERP responses. Task-related strategies did not differ between groups. The pattern of AERP amplitude asymmetry found for disabled readers, which was opposite to that found for normal readers, suggests that the same reading-related tasks activated different cerebral processes in the two groups studied.     

Event-related potentials and the semantic matching of pictures

Event-related potentials (ERPs) were recorded from one midline and three pairs of lateral electrodes while subjects determined whether pairs of sequentially presented pictures were semantically associated. The ERPs evoked by the second picture of each pair differed as a consequence of whether it was associated with its predecessor, such that ERPs to nonassociated pictures were more negative-going than those to associated items. These differences resulted from the modulation of two ERP components, one frontally distributed and centered on an N300 deflection, the other distributed more widely over the scalp and encompassing an N450 deflection. The modulation of N450 is interpreted as further evidence that the "N400" ERP component is sensitive to semantic relationships between nonverbal stimuli. The earlier N300 effects, which do not appear to occur when ERPs are evoked by semantically primed and unprimed words, could suggest that the semantic processing of pictorial stimuli involves neural systems different from those associated with the semantic processing of words.     

Self-posed behaviors of females and males in photographs

In a previous study, Ragan (1982) found systematic sex differences in the poses of persons photographed by professional photographers. In this study, 34 female and 34 male subjects posed themselves for a confederate, allegedly a photography student, who took the photographs from which data were drawn to assess sex differences in self-posed photographs. A MANOVA revealed overall significance with females smiling, canting, and orientating away from the camera more than males. An ANOVA produced significant sex differences for only the smiling data. Results are discussed in terms of Goffman's (1976) suggestion that photographers introduce their distortions into photographs and in terms of Duval and Wicklund's theory of objective self-awareness (1972).The author gratefully acknowledges the photographic assistance of Pam Bugg, Clay Langley, Jim Hamilton, and Susan Moore.     

Event-related brain potentials elicited during word recognition by adult good and poor phonological decoders

Cognitive processing of lexical and sub-lexical stimuli was compared for good and poor adult phonological decoders. Sixteen good decoders and 16 poor decoders, average age 19 years, silently read 150 randomly computer presented sentences ending in incongruous regular, irregular, or nonwords and 100 congruent filler sentences. Electro-encephalographic recordings were made from the final word of each incongruous sentence. Although no significant group differences were found, good decoders showed specialised hemispheric word recognition processing at P200 and P300. Nonwords elicited greater N200 and P300 amplitudes for both good and poor decoders. Larger amplitude P200s were elicited by poor decoders when processing nonwords. These findings provide evidence for separable lexical and sub-lexical procedures and support a psychophysiological basis for a core phonological deficit in poor phonological decoders.