AVERAGE EVOKED RESPONSE AND VERBAL CORRELATES OF UNCONSCIOUS MENTAL PROCESSES

Two methods for identifying visual average evoked response components—one based on sequence, the other on peak amplitude—resulted in significant discriminations between subliminal visual stimuli, thus supporting and extending previous findings dealing with the investigation of unconscious mental processes. In addition, verbal effects of a subliminal stimulus, detected by a free association procedure, were found, which correlated with different AER characteristics. Verbal effects which were conceptually and veridically related to the stimulus correlated with an AER amplitude component (90–260 msec post-stimulus), while homophonic, unveridical verbal effects were related to the incidence of alpha bursts approximately 1 1/2 sec post-stimulus. Ss were 12 pairs of twins, ranging in age from 13–22. For older Ss (17–20) the sequence and peak amplitude components coincided; for younger Ss (12–16), they were different. Younger Ss also had significantly larger amplitudes than older Ss for both subliminal and supraliminal conditions (peak amplitude method) and for the supraliminal condition (sequence method).     

The Effects of Attention, Stimulus Intensity, and Individual Differences on the Average Evoked Response

The effects of shifting attention toward or away from visual or auditory stimuli of varying intensities were studied using average evoked responses (AERs) in 24 normal human volunteers. Ss were asked to attend to visual or auditory stimuli of four intensities (randomly presented) or to ignore the lights and tones and do mental arithmetic. For visual stimuli, attentional effects were largest at low intensities whereas for auditory stimuli equal effects were shown across intensities. Similar individual rates of increase of AER amplitude with increasing intensity were observed for both visual and auditory stimuli when attentional conditions were controlled. These results suggest that some general intensity processing response is reflected in the AER and that it is important to control attention in AER experiments.     

The Effect of Predictability on Evoked Response Enhancement in Intramodal Selective Attention

We investigated the relationship between the attention enhancement of the visual average evoked response (AER) and the S's ability to predict the presentation of the attended stimulus. Twelve students were presented with sequences of two distinct visual stimuli while DC EEG and electro-oculogram (EOG) were simultaneously recorded. Stimuli were either regularly alternated (predictable) or randomly intermixed (nonpredictable). Verbal instructions directed S's attention and push button response to either one or both of the two stimuli. Interstimulus interval was held constant to permit computer averaging of the AER and the contingent negative variation. Selective attention enhanced the late positive component of the AER equally in the two conditions of predictability. Thus, it seems that the AER enhancement with intramodal selective attention does not depend on the S's ability to predict the presentation of the attended stimulus or to differentially arouse prior to its presentation. In the high predictability condition, the baseline EEG potential fluctuated with attention such that the AERs to the attended stimuli were negative relative to those to the ignored stimuli.     

Awakening Latency From Sleep For Meaningful and Non-Meaningful Stimuli

Personally significant and non-significant low intensity sound stimuli were used to determine awakening latencies from sleep stages REM and 2. Latency was measured from stimulus onset to a) the sleeper's own acknowledgement of waking, and b) alpha rhythm onset. Both stimuli were presented twice, once in each sleep stage, to 8 Ss. Voluntary response latencies in REM were shorter than in stage 2 (p <.025) but no difference was found for the latency of alpha rhythm onset. The personally significant stimulus, however, caused a significantly shorter awakening latency using both criteria. The results suggest that perceptual thresholds are low in both sleep stages 2 and REM but that the ability or willingness to organize a response is greater in REM sleep.     

Amplitude and Habituation of the Orienting Reflex as a Function of Stimulus Intensity

Two within-S experiments involving 20 Ss each and one between-S experiment employing 100 Ss were performed to examine effects of stimulus intensity on orienting response amplitude and habituation. Five intensities of a 1000 Hz tone were presented, ranging from 0 to 40 dB in Experiment I and from 0 to 80 dB in Experiments II and III. Response measures were skin conductance response (SCR) and heart rate (HR). Skin conductance response amplitude increased monotonically with stimulus intensity while HR deceleration was a generally decreasing function which tended to decrease, increase, and finally decrease again as intensity increased. Not only was deceleration greatest at 0 dB but it was more resistant to habituation. Several intensities of test stimulation were presented after habituating stimuli in the between-S experiment. Skin conductance response to test stimuli was facilitated by habituation at 0 dB and depressed by habituation at 80 dB. The results suggest a direct relationship between stimulus intensity and development of habituation.     

CORTICAL EVOKED POTENTIALS TO SEMANTIC STIMULI

The influence of affective meaning on the photically evoked response was studied in male college students. Three sets of stimuli were used: taboo words, neutral words, and blank flashes. Two blocks of trials were run for each stimulus, one in which the S responded by calling the stimulus presented, and a second in which the S was not required to respond. The late components of the evoked potential were significantly related to both the stimulus and response conditions. Amplitude 2 was larger for the taboo words than for either the neutral words or the blank flash. The taboo words had a significantly greater amplitude 3 than neutral words, and both sets of words had higher amplitude 3 than the blank flash. The stimulus effect was discussed in terms of the possible influence of anatomical structures involved in emotional behavior on the visual evoked response. The response effect was felt to be the result of the increased attention required under the response condition.     

THE INFLUENCE OF SOME PSYCHOLOGICAL FACTORS ON LATENCY OF THE GALVANIC SKIN REFLEX

The purpose of this study was to examine the effect of differences in motivativation and in attention on latency of the endosomatic GSR. Using verbal instructions, two different levels of motivation were induced in a group of 37 Ss who performed a simple reaction task in which they pressed a button whenever a 250 cycle tone was presented. The same tone also served as a stimulus for eliciting the GSR. In a second experiment, 42 different Ss performed a similar reaction task, but in this case the stimulus was the 250 cycle tone or a 1,000 cycle tone of equal subjective intensity. Ss were asked to give a voluntary response to all tones irrespective of frequency and then, later on, to respond only when the 1,000 cycle tone was presented. Although voluntary reaction times were significantly shorter under conditions of high as compared with low motivation, latency of the GSR did not differ for the two conditions. In the second experiment, significantly shorter GSR latencies were recorded under the condition where Ss were required to pay closer attention to the stimulus.     

THE USE OF ELECTRO-OCULOGRAPHY FOR IDENTIFYING PHASES OF COGNITIVE PROCESS

The present investigators were partly concerned with possible uses of electro-oculography for studying the cognitive process in decision-making situations involving nonneutral visual stimuli. S was faced with receiving an electric shock if on critical trials he correctly reported (manually) the identity of the visual stimulus, or with escaping shock by incorrect reporting. Electrooculogram responses were ascertained to identify eye movements. The first study employed slit geometric figures as critical stimuli and nonslit figures as noncritical stimuli. The second study differed only in using blanks as critical and nonblanks (figures) as noncritical stimuli. The 80 males in the first study showed longer ocular latency, then greater ocular avoidance (narrower excursions) but longer stimulus viewing, then longer poststimulus viewing on critical compared to noncritical trials. The 25 males in the second study showed relatively greater ocular latency, then greater ocular avoidance and briefer stimulus viewing, then briefer poststimulus viewing on critical trials. Discrepancies between the two studies were discussed. The results clearly indicate the applicability of electrooculography for identifying phases of cognitive process.     

PERSONALITY AND AROUSAL CORRELATES OF SPECIFIC GALVANIC SKIN RESPONSES

Basal skin resistance (BSR) and galvanic skin responses (GSR) to five intensities of sound and light were recorded on four occasions in 32 student subjects (Ss). These occasions were assumed to include unfamiliarity and basal and real life stress conditions. All Ss completed the MMPI, California Personality Inventory, Wechsler Adult Intelligence Scale, Clyde Mood Scale and Examination Anxiety Scale. GSR amplitude was greater under conditions of unfamiliarity, alertness (by electroencephalographic criteria), and higher intensities of stimulation in both stimulus modalities. It was not greater during the presumed stress period. High ego strength-high Barrier score Ss showed a greater GSR amplitude than low ego strength-low Barrier Ss. Test indices of anxiety generally were not related to GSR amplitude, nor were other personality and mood variables.     

Overextinction of the Evoked Skin Conductance Response: An EEG Study

The present study was designed to investigate Sokolov's (1963) proposal that overextinction of the orienting response (OR) is related to sleep onset. A series of 80 auditory stimuli was presented to 22 male and female Ss. Although re-evocation of the skin conductance response (SCR) component of the OR occurred, in the majority of Ss, after 40–50 stimulus presentations, this was not accompanied by any change in cortical alertness as measured by integrated EEG output in three frequency bands (2–4, 4–8, and 8–13 Hz). However, the results did indicate that Ss displaying SCR return required more stimulus presentations before initial SCR habituation and displayed more spontaneous fluctuations in skin conductance during the prestimulus period than did non-return Ss. Within the return group, latency of SCR return was negatively related to both spontaneous activity during the prestimulus period and number of stimuli to initial habituation.     

Prevalence and Methods of Control of the Cephalic Skin Potential EEG Artifact

Prevalence of the cephalic skin potential (CSP) artifact was studied in 21 Ss during EEG recording of the Contingent Negative Variation (CNV), averaged evoked response (AER), and verbal free association test. Skin potential response and electro-oculogram (EOG) were also recorded. Subdermal pin electrodes and local anesthesia infusion were employed to eliminate the CSP artifact in the EEG. Results indicated that EEG recorded from subdermal pin electrodes or from locally anesthetized scalp was free of CSP artifact. The EEG recorded from subdermal pin electrodes demonstrated spontaneous potential shifts but appeared adequate for EEG recording of the CNV or the AER. Significant CSP artifact was demonstrated in the EEG of 10 of 21 Ss, both evoked by stimuli (10 Ss) and spontaneous (3 Ss). CSP artifact significantly increased CNV amplitude. CSP artifact significantly increased the AER late positive wave (P3) to infrequent tones. Studies of CNV and AER can be confounded by CSP artifact. Above techniques appear promising for recording EEG free of CSP artifact.     

RESPIRATION AND SUCKING AS COMPONENTS OF THE ORIENTING REACTION IN NEWBORNS

Respiratory and non-nutritive sucking responses to auditory stimulation were studied in 1- to 5-day old human newborns. Each S was presented 5 stimuli, each 4 times, during 4 sessions at 24 hour intervals. The stimuli varied in intensity and intermittency. Stimulus onset and offset shortened sucking bursts during Sessions I-III, but in Session IV stimulus offset lengthened sucking bursts. In general, respiration was accelerated by stimulus onset and decelerated by stimulus offset. However, in Session IV respiratory deceleration occurred to both stimulus onset and offset. Respiratory deceleration also occurred to low intensity stimuli in Sessions I-III. Respiratory acceleration and sucking inhibition were discussed as components of the newborn's defense reaction (DR) to most stimulation. Respiratory deceleration was related to appearance of orienting reaction (OR) after habituation of DR. Ss' respiratory responsivity and sucking responsivity were highly correlated.     

Auditory Evoked Responses to Unpredictable Stimuli

The auditory evoked response (AER) to unpredictable stimuli was studied in 18 Ss. 100 msec sound bursts consisting of either a pure tone or white noise were presented every sec. One type of stimulus constituted the frequent expected stimulus and the other the infrequent stimulus that occurred as a random substitution. For the low probability (LP) stimulus condition, the mean ratio of infrequent to frequent was 1:30; for the intermediate probability (IP), 1:15; and for the high probability (HP), 1:7.5. Ss were instructed to ignore the sounds. The amplitude of a late positive wave (P3) of the AER was largest in the LP and smallest in the HP condition. There was a general decrease of all AER components over the course of a session. No evidence of dishabituation in the AER to the stimuli following the infrequent stimuli was obtained. The results of a detailed analysis of two orbital leads make it unlikely that eye movement or eye blink could account for the results.     

THE INTERACTION OF RESPONSES IN THE BRAIN TO SEMANTIC STIMULI

Long time-constant EEG recording during paired stimuli has led to the discovery of the contingent negative variation or expectancy wave (Walter, 1964). This effect is produced when a conditional stimulus signals that an imperative stimulus demanding action, decision, or attention will follow at a short, constant time interval. Symbolic and meaningful stimuli were presented to subjects tachistoscopically, and the evoked responses in the brain were electronically averaged. The cerebral evoked responses to such psychological stimuli are more complex than to flashes. A slow negative DC potential shift (CNV) was seen during the interval between an auditory ready signal and the visual exposure if recognition of the stimulus was required, or if it was interesting. Following the visual exposure, a slow positive DC shift occurred. The method has been developed to study the brain responses to psychological stimuli. The amplitude of the responses relates to the information content and subjective factors rather than to the physical strength of the stimulus.     

Event-related potential correlates of non-motor anticipation.

A slow negative shift called "stimulus-preceding negativity" (SPN) has been observed preceding feedback. The aim of the present study is to investigate whether the SPN is related to perceptual or conceptual anticipation. Event-related potentials (ERPs) were recorded in an S1-S2-S3 sequence with intervals of 3 s. S1 was an auditory warning signal; the task stimulus presented at S2 consisted of two digits on which subjects (n = 8) performed an arithmetic task. They had to match their solution with a probe stimulus presented at S3. Perceptual anticipation was manipulated by varying the discriminability of S2 (intact vs. degraded). Conceptual anticipation was manipulated by varying the amount of information processing required at S2 (easy vs. difficult arithmetic). Motor preparation was varied by requiring a speeded versus a delayed response. No negativity was found before the task stimulus (S2), whereas the probe stimulus (S3) was always preceded by a negative shift. The amplitude of this negative shift was larger under the speed than under the delayed instruction. Its amplitude showed a left-hemisphere preponderance and was larger for the difficult than for the easy condition. ERPs preceding task stimuli seem to reflect functionally different processes from ERPs preceding probe and feedback stimuli. The difference is explained in terms of motivational factors that come into play with feedback and probably play a role in the anticipation of the probe stimulus.     

Target-to-target interval, intensity, and P300 from an auditory single-stimulus task

Target-to-target interval (TTI) is a primary determinant of P300 amplitude, such that longer TTIs yield larger components than shorter intervals. Systematic manipulations of TTI affect component amplitude, latency, and associated response time in a fashion that suggests that the template update hypothesis can account for these outcomes. The present study examines whether manipulations of TTI (from 1 to 16 s) and stimulus intensity (soft and loud tones) produce outcomes consistent with this hypothesis. A single-stimulus task was employed in which only target stimuli were presented. P300 amplitude increased, peak latency decreased, and response time increased as TTI became longer, with less effect for soft compared to loud stimulus conditions on P300 amplitude at Pz. TTI increases also augmented N100 amplitude, with consistently smaller amplitudes obtained for soft relative to loud stimuli. Overall, P300 measures are sensitive to both temporal and physical stimulus factors. Theoretical implications are discussed.     

Effect of configural distortion on a face-related ERP evoked by random dots blinking

Using random dots blinking (RDB), which reflects the activity of the higher visual area related to face perception, the following stimuli were presented. (1) Upright: a schematic face; (2) Inverted: the Upright stimulus inverted; and (3) Scrambled: the same contour and features as in Upright but with the spatial relation distorted. Clear negative components (N-ERP250) were identified at approximately 250 ms after stimulus onset. At the T5 and T6 electrodes, the peak latency was significantly longer for Inverted and Scrambled than for Upright. At the P4 electrode, the maximum amplitude was significantly larger for Scrambled than for Upright and Inverted. These results indicate that the delayed latency for Inverted and Scrambled reflects the involvement of the additional analytic processing caused by the configural distortion, and that the increase in amplitude for Scrambled indicates the existence of further processing caused by the distortion of the spatial relationship between the contour and features.     

Spatial orienting and focused attention in attention deficit hyperactivity disorder

Seventeen children with attention deficit disorder (ADHD) and 10 normal controls performed two tasks while event-related potentials were recorded. ADHD subjects took part in two more sessions under methylphenidate (MP) or placebo. In the spatial orienting task, invalidly cued targets elicited a longer reaction time (RT) and a P₃ that was longer in latency and greater in amplitude than did validly cued targets. Performance was similar for both groups, but the early portion of P₃ (300–400 ms) was lower in amplitude for invalidly cued targets in ADHD subjects. MP increased accuracy without affecting RT and shortened P₃ peak latency and increased the amplitude of its early portion. In the focused attention task, accuracy was greater for controls and MP, but there were no RT differenees. Attended stimuli elicited greater amplitude P₁, N₁, and P₃ than did nonattended stimuli, but these measures were unaffected by diagnosis or medication.     

The effects of covert attention and stimulus complexity on the P3 response during an auditory continuous performance task.

This study examined the effects of motor responding and stimulus complexity on the event-related potential (ERP) P3 amplitude and latency during an auditory continuous performance task (A-CPT). Subjects were presented with undegraded and degraded syllables during two experimental conditions. In the motor attention (MA) condition participants performed a button press to target syllables. In the covert attention (CA) condition, participants listened for target syllables without responding. The ERP P3 amplitude for targets during MA and CA showed the expected anterior-to-posterior scalp topography, with the greatest amplitude at Pz. Although amplitudes across all scalp sites were greater for MA than CA target P3 responses, both MA and CA targets had greater P3 amplitudes than the P3 for the nontarget syllables (NT). There was no effect of stimulus complexity (degraded vs. undegraded) on P3 amplitude. However, stimulus complexity did affect P3 latency. Degraded syllables elicited longer P3 latency than undegraded syllables for both the MA and CA conditions. The amplitude and topography findings show that when stimulus probability is controlled through the use of a CPT paradigm, a reliable P3 component is present even when the task does not require a motor response to target stimuli.     

Subjective and Response-Related Determinants of CNV Amplitude

The effect on contingent negative variation (CNV) of varying the difficulty of obtaining reaction time (RT) feedback and the relationship of CNV and RT were studied. Subjects (Ss) were run in a reaction-time-foreperiod experiment with 4 conditions of varying RT feedback duration. Subjective reactions to the experiment were recorded by Ss on a questionnaire and were divided by the experimenters into two highly significant sets of mean CNVs based on the most “positive’ and most “negative’ responses to the conditions. CNVs and their associated RTs were analyzed, and a significant rank order correlation over all Ss showed there was a trend for individuals with faster RTs to have larger CNVs. Individual correlations were low and highly variable. Only the very slowest RTs were associated with small CNVs. The failure of explicit RT feedback to have any effect upon CNV amplitude is in agreement with previous studies, and the significant association of CNV amplitude with written reactions of Ss might prove a useful tool for further CNV analysis. The RT data indicated that CNVs and RTs reflect relatively independent functions and that very slow RTs may reflect qualitative changes in S's psychological state which affect both RT and CNV; and such trials might appropriately be eliminated from CNV data analysis.