Habituation and the human evoked potential

Habituation of human scalp-recorded cerebral evoked potentials was studied in response to auditory and visual repetitive stimuli of different intensities. Changes in magnitudes of evoked potentials with stimulus repetition were examined according to the parametric characteristics of habituation, generalization, and dishabituation. In addition, tests of the predictions of two theories of habituation were made regarding the degree and direction of intensity generalization of habituation. Both auditory and visual evoked potentials exhibited decrements in response magnitudes across the repetitive stimuli consistent with the parametric criteria of habituation. Early evoked potential peak components showed a pattern of intensity generalization of habituation consistent with the predictions of the dual-process theory of habituation. Intensity generalization of late evoked potential peak components occurred in a manner more consistent with the predictions of the stimulus comparator theory of habituation. These results provide further evidence that evoked potentials can be used as electrophysiological indexes of plasticity in humans.     

EEG characteristics prior to and following the evoked K-Complex.

This study was designed to determine if the K-Complex reflects an arousal from sleep or a sleep protection mechanism. Ten participants were presented auditory stimuli every 20 s while asleep. Trials were sorted according to the presence or absence of a K-Complex. A fast Fourier Transformation of the data was computed on EEG segments prior to and following stimulus onset. The log power of activity in delta, theta, alpha, sigma, and beta bandwidths was computed. When a K-Complex was elicited, there were no differences in EEG activity prior to and following the stimulus. However, during slow wave sleep, when a K-Complex was not elicited, there was a significant overall increase in theta, alpha, sigma, and beta activity following stimulus. These results tend to support the notion that the K-Complex appears to prevent arousal.     

An event-coder for evoked potential studies

A device is described which has 10 input and 2 output lines. Grounding an input causes a pulse with a specific amplitude, polarity, and duration to appear on one of the output lines. Pulse parameters can be set by front-panel controls. Thus, 10 distinct events can be coded by associating a unique pulse with each event. These pulses can be recorded on one (or two) channels of a magnetic tape recorder for subsequent processing. The use of this coder in the study of event-related potentials is described.     

Early selective-attention effect on evoked potential reinterpreted

In a dichotic listening situation stimuli were presented one at a time and at random to either ear of the subject at constant inter-stimulus intervals of 800 msec. The subject's task was to detect and count occasional slightly different stimuli in one ear. In Experiment 1, these ‘signal’ stimuli were slightly louder, and in Experiment 2 they had a slightly higher pitch, than the much more frequent, ‘standard’, stimuli. In both experiments signals occured randomly at either ear. Separate evoked potentials from three different locations were recorded for each of the four kinds of stimuli (attended signals, unattended signals, attended standards, unattended standards). Contrary to Hillyard et al. (1973), no early (N₁ component) evoked-potential enhancement was observed to stimuli to the attended ear as compared with those to the unattended ear, but there was a later negative shift superimposed on potentials elicited by the former stimuli. This negative shift was considered identical to the N₁ enhancement of Hillyard and his colleagues which in the present study was forced, by the longer inter-stimulus interval used, to demonstrate temporal dissociation with the N₁ component. The ‘Hillyard effect’ was, consequently, explained as being caused by a superimposition of a CNV kind of negative shift on the evoked potential to the attended stimuli rather than by a growth of the ‘real’ N₁ component of the evoked potential.     

Binocular summation in the evoked cortical potential

Computer-averaged evoked potentials were recorded from six subjects presented with flashes under conditions of binocular and monocular viewing, with a device fitted over each eye to produce ganzfeld conditions. Tests were run with red light and with blue. Analysis of the evoked potentials indicates a substantially larger amplitude with binocular stimulation.     

Cortical evoked potential, personality, and intelligence.

The averaged cortical evoked potential (CEP) was measured from 296 male subjects in two studies and was correlated with scores on intelligence and personality tests. For both studies, auditory stimuli were used with bipolar electrode placement to the Cz and T3 scalp positions. In the first study, with 84 subjects, stimulus intensity was 95 dB (all dB readings re 20 muN/m2). Intelligence was measured with the Mill Hill Vocabulary Scale and personality with H. J. Eysenck's PEN questionnaire. The second study, with 212 subjects, used additional stimuli at 75 dB and 55 dB. Intelligence was measured with the Ravens Progressive Matrices. State anxiety and other state measures at the time of testing were also taken. Neither study found any relation between the CEP and IQ or personality. However, more bored subjects showed larger CEP amplitudes. The results are discussed in terms of Ertl's neural efficiency hypothesis and Eysenck's arousal theory of personality.     

Acoustically evoked brain stem potential in Wilson disease

By 48 patients with Wilson's disease the brainstem acoustic evoked potentials were stated. There were 35 pathological findings (73%), 13 were normal (27%). The waves, determined by the middle and upper brainstem (Pons and Mesencephalon) showed most of all pathological changes. Those patients with forms of Wilson's disease called Pseudoskelerose and Pseudoparkinson showed the most pathological findings. But one could watch these findings by about 30% of patients in preclinical stage. This method can possibly be used for early detection of disorders of brainstem functions and in the same way it can be used for control of treatment by patients in preclinical stage.     

A general framework for defining evoked potential paradigms

We have developed a framework for defining a range of evoked potential paradigms through the completion of screen forms rather than through the modification of program code. Within this framework, an experimenter can specify stimulus events and their timing, randomization of different stimuli, collection of responses, rejection of artifacts, and detection of peaks within the averaged waveforms. Printed copies of the screen forms and of timing diagrams derived from them can later be incorporated into the documentation of the experiment.     

Auditory evoked potential correlates of speech sound discrimination

An electrophysiological correlate of the discrimination of stop consonants drawn from within and across phonetic categories was investigated by an auditory evoked response (AER) technique. Ss were presented a string of stimuli from the phonetic category [ba] (the standard stimulus) and were asked to detect the occurrence of a stimulus from the same phonetic category (within-category shift), or the occurrence of a stimulus from a different phonetic category [pa] (across-category shift). Both the across- and within-category shift stimuli differed equally from the standard stimulus in the time of onset of the first formant and in the amount of aspiration in the second and third formants. The NIP2 response of the AER was larger to the across-category shift than to the within-category shift. The within-category shift did not differ from a no-shift control. These findings suggest (1) that the AER can reflect the relative discriminability of stop consonants drawn from the same or different phonetic categories in a manner similar to other behavioral measures; (2) that the detailed acoustic representation of stop consonants is transformed into a categorized phonetic representation within 200 msec after stimulus onset.     

The semantic component of the evoked potential of differentiation

This work analyzes data from recordings of (occipital and temporal) cortical evoked potentials (called evoked potentials of differentiation (EPD) occurring in humans in response to an abrupt substitution of stimuli. As stimuli we used three groups of words: the names of the ten basic colors taken from Newton's color circle; the names of seven basic emotions forming Shlossberg's circle of emotions; and seven nonsense words comprised of random combinations of letters. Within each group of word stimuli we constructed a matrix of the differences between the amplitudes of mid-latency components of EPD for each pair of words. This matrix was analyzed using the method of multidimensional scaling. As a result of this analysis we were able to distinguish the semantic and configurational components of EPD amplitude. The semantic component of EPD amplitude was evaluated by comparing structure of the data obtained to the circular structures of emotion and color names. The configurational component was evaluated on the basis of the attribute of word length (number of letters). It was demonstrated that the semantic component of the EPD can only be detected in the left occipital lead at an interpeak amplitude of P120-N180. The configurational component is reflected in the occipital and temporal leads to an identical extent, but only in the amplitude of a later (N180-P230) component of the EPD. The results obtained are discussed in terms of the coding of categorized, configurational, and semantic attributes of a visual stimulus.     

A steady state visually evoked potential investigation of memory and ageing

Old age is generally accompanied by a decline in memory performance. Specifically, neuroimaging and electrophysiological studies have revealed that there are age-related changes in the neural correlates of episodic and working memory. This study investigated age-associated changes in the steady state visually evoked potential (SSVEP) amplitude and latency associated with memory performance. Participants were 15 older (59–67 years) and 14 younger (20–30 years) adults who performed an object working memory (OWM) task and a contextual recognition memory (CRM) task, whilst the SSVEP was recorded from 64 electrode sites. Retention of a single object in the low demand OWM task was characterised by smaller frontal SSVEP amplitude and latency differences in older adults than in younger adults, indicative of an age-associated reduction in neural processes. Recognition of visual images in the more difficult CRM task was accompanied by larger, more sustained SSVEP amplitude and latency decreases over temporal parietal regions in older adults. In contrast, the more transient, frontally mediated pattern of activity demonstrated by younger adults suggests that younger and older adults utilize different neural resources to perform recognition judgements. The results provide support for compensatory processes in the aging brain; at lower task demands, older adults demonstrate reduced neural activity, whereas at greater task demands neural activity is increased.     

Hypnotic suggestion of stimulus change and visual cortical evoked potential.

Two experiments were conducted to determine whether the hypnotic suggestion of stimulus intensity change would affect the physical parameters (latencies, amplitudes) of the visual cortical evoked potential. Stimulus intensity was kept constant as visual cortical evoked potentials were measured under conditions in which it was suggested that stimuli were "bright" or "dim". The results of both experiments led to the conclusion that, under the present condition, hypnotic suggestion of stimulus intensity change did not result in changes in visual cortical evoked potentials.     

The impact of prestimulus EEG frequency on auditory evoked potentials during sleep onset.

Auditory evoked potentials were recorded during wakefulness, Stage 1, and Stage 2 non-REM sleep using a three-tone auditory oddball paradigm. Stage 1 sleep was divided into trials preceded by alpha and those preceded by theta. A negative wave peaking at about 100 ms, N1, displayed a significant decrease in amplitude with the onset of Stage 2 sleep. A later N2 peaked at about 250 ms in the waking state. This changed into a sleep-specific negative wave peaking at 300 ms (N300) at the alpha-theta transition within Stage 1. The P300 displayed a similar shift to become a P450 in Stage 2 sleep. N550 was specific to Stage 2, and was larger in response to rare, rather than frequent stimuli. There was no evidence of any enhancement to relevant rare stimuli compared with irrelevant rare stimuli.     

Response and evoked potential latencies associated with commission errors in visual monitoring

Attention, Perception, & Psychophysics - Eight male subjects performed a 40-min visual monitoring task in which they were required to detect the occasional dim flash from a background of...