GSR amplitude instead of GSR magnitude: Caveat emptor!

Size of GSR made by 300 Ss to 20 repetitions of a visual stimulus is presented as mean magnitude and mean amplitude, illustrating that the amplitude method (averaging only those responses which are greater than zero) is susceptible to distortion resulting from a systematic elimination of Ss who initially make small responses. From trial to trial, the amplitude function comes more and more to be due to the behavior of Ss who initially make large responses. Even though the latter Ss’ responses actually reduce across trials, the amplitude function rises. Magnitude (including zeroes) docs not suffer from this distortion. It is suggested that the definition of a zero response is the source of the problem.     

P300 and probability in children

The P300 event-related brain potential (ERP) was elicited in three groups of 12 children each, ages 5-9, 10-14, and 15-19 years. A simple auditory task was employed in which subjects indicated with a finger movement when a randomly occurring target tone (high pitch) was presented in a series of standard (low pitch) tones. The probability of the target tone was varied across conditions at 0.10, 0.30, or 0.50 to determine if P300 amplitude would respond similarly across age groups. Immediate memory capacity was measured with forward and reverse digit spans. P300 amplitude increased with decreases in target stimulus probability for each age group and also tended to become larger with age. P300 latency decreased in the same fashion across probability levels as age increased. Digit span demonstrated the usual increase with age. The results suggest that cognitive development is indexed by decreases in P300 latency, and that P300 amplitude changes from the probability of the target stimulus are similar across age groups. The implications for the theoretical interpretation of the P300 and application of ERPs for evaluating cognitive development are discussed.     

Effects of phase-of-respiration on GSR detection

Previous studies of visual and auditory signal detection (Flexman & Demaree, 1972; Flexman, 1974; Flexman, Demaree & Simpson, 1974) have found that signals occurring during exhalation are detected with greater sensitivity than are signals occuring during inhalation. The purpose of the present study was to make use of a use of a signal detection paradigm (Green & Swets, 1966) in extending these phase-of-respiration findings to internal event detection, specifically, to the detection of spontaneous galvanic skin responses (GSRs). A secondary purpose of the study was to re-examine Stern's (1972) finding that high magnitude GSRs were better detected than were low magnitude GSRs. It was found that the phase of respiration during which the GRS reached its peak significantly influenced GSR detection, but that unlike studies of external signal detection, detection was greater for GSRs peaking during the inhalation than for GSRs peaking during exhalation. Some possible artifactual sources of this finding are discussed. No significant effect of GSR magnitude on GSR detection was observed although differences were in the expected direction.     

Evoked potentials to consonant-vowel syllables

The hypothesis was tested that CV syllables (10 different consonants but the same vowel /?/) would show different evoked potential latencies and amplitudes. Differences were found which were dichotomised between plosives and other consonants. Although one difference between these two groups of consonants is the duration of that consonant, this duration difference did not adequately explain the prolonged evoked potential latencies and the reduced amplitudes for the non-plosives. However, no differences were found within the group of non-plosives, although they varied in consonant duration. It was suggested that N₁ latency and amplitude reflected processing time at an early stage of analysis of both speech and non-speech stimuli. The results show that consunants of long duration are perceived later than plosives, but well before the onset of the vowel.     

Long latency auditory evoked potentials

Experiment 1 elicited the P1, N1, P2, and N2 components of the long latency auditory evoked potential (AEP) using a 1000 Hz tone presented at 30, 50, or 70 dB SPL and 1-, 3-, or 5- second inter-stimulus intervals to assess the relative effects of the combination of these variables on component amplitude and latency. Four blocks of 16 tone presentations each were recorded from each subject to determine if changes in the AEP would occur because of short-term habituation. Both stimulus factors interacted significantly in a systematic fashion for the amplitude measures, with increases in latency also associated with increases in intensity and inter-stimulus interval. Only minor changes across the four trial blocks for either the amplitude or latency measures were observed over the various stimulus presentation conditions. Experiment 2 employed the same tone stimulus presented at 50 dB SPL and a 3-second inter-stimulus interval. Eight blocks of 64 trials were recorded from each subject on each day for four days to investigate long-term habituation effects. No substantial changes in any of the component amplitudes or latencies were obtained across the 32 trial blocks. It was concluded that intensity and inter-stimulus interval interact to determine AEP amplitude as well as latency values and that the constituent components do not change appreciably with repeated stimulus presentations, even after several days.     

Effects of tobacco smoking on electroencephalographic, auditory evoked and event related potentials

After overnight abstinence, tobacco smokers smoked an average nicotine yield cigarette and nonsmokers sham smoked an unlit placebo cigarette. EEG alpha(1), delta, and theta frequency amplitudes decreased, whereas alpha(2) and beta frequency amplitude increased. Short, middle (EP) and long latency ERP were also studied in nonsmokers and smokers just after smoking, and after overnight abstinence from tobacco. Short latency potentials were unaffected by tobacco smoking or abstinence. Middle and long-latency potentials were reduced during abstinence and enhanced immediately after tobacco smoking. These findings indicate that compared to nonsmokers smokers have a higher arousal level after smoking than when partially abstinent. Evidence for both normalization from tobacco abstinence as well as stimulation was obtained.     

The mental number line electrified: brain potentials in a numerical flanker task

It has been suggested that the mental representation of numbers is spatial in nature such that numbers are ordered on a mental number line. In the present investigation we use a variant of the Eriksen flanker task requiring a magnitude decision (smaller or larger than 5) for a central target number by pressing a response button with the right or left hand. The target number is flanked by irrelevant distracters that are either identical to the target, different from the target but biasing the same response, or different from the target and biasing a different response. Response latencies and event-related brain potentials were obtained in a group of healthy adults. Besides the typical response congruency effects on response latency and the N2 component of the ERP, we observed several other effects. First, numerical distance of the target to the standard 5 influenced decision latencies and amplitude and latency of the P3 component with smaller distances leading to longer decision latencies, longer P3 latencies and smaller P3 amplitudes. Second, smaller numerical distance between target and distracters led to faster decisions for response congruent and to slower decisions for response-incongruent trials. For response-incongruent trials P3 amplitude was small/large and P3 latency was long/short for small/large distances. These findings underscore the spatial character of number representation and further show that the relation between targets and distracters, although task irrelevant, is assessed automatically with facilitatory and inhibitory effects driven by spatial distance on the mental number line.     

Cerebral evoked responses in schizophrenia

Results of previous studies of evoked responses in schizophrenic disorders are reviewed, and data from a new study of somatosensory recovery functions in schizophrenia are presented. Subjects in the latter study were 18 schizophrenic patients and 18 nonpatients matched for age and sex. Latencies and amplitudes of eight consecutive evoked-response peaks were measured. Only one amplitude and one latency of the response to the first stimulus discriminated between patients and controls, whereas four amplitudes and three latencies of the second response did so. Amplitude recovery was less in patients, whereas latency recovery was greater. The data verified previous findings of impaired amplitude recovery in schizophrenia, but did not confirm previous findings of increased amplitude in response to a single stimulus. Evoked-response deviations so far determined are not specific to schizophrenic disorders, inasmuch as they have been found in several other psychiatric syndromes. The data are in accord with the idea that psychiatric disorders involve deviant cerebral processing of sensory information.     

The separate and combined effects of GSR biofeedback and delayed auditory feedback on stuttering: A preliminary study

The separate and combined effects of galvanic skin response biofeedback low wave amplitude self regulation (GSR LW) and amplified delayed auditory feedback (DAF) upon stuttering dysfluency are examined. Two college age male stutterers who were seen on an intensive longitudinal basis were the subjects in this study.Results suggest that GSR LW, when it is accomplished, functions to moderately but significantly reduce stuttering dysfluency compared to no GSR biofeedback. This effect does not noticeably dissipate over time. There occurred a marked and sustained reduction in stuttering dysfluency under DAF compared to no DAF conditions. Without separating accomplished and not accomplished GSR LW, there occurred slightly but not statistically significantly fewer blocks under the combined DAF-GSR LW condition than under DAF alone. Nevertheless, it does seem likely, considering these findings overall, that when GSR LW is accomplished, the fluency facilitating effect of its simultaneous combination with DAF is additive i.e., greater than either alone. Possible theoretical and therapeutic implications are discussed.     

State-dependent variations in brainstem auditory evoked responses in human subjects

BAERs from 16 subjects during 3 sessions varied in the latency or amplitude of some components depending upon level of arousal as indicated by EEG patterns. There was a general tendency for activation to produce the fastest responses with the largest amplitudes and for drowsiness to produce the slowest responses with the smallest amplitudes. The latency of P2 was significantly prolonged during drowsiness, relative to those during relaxation or activation. For right-ear stimulation, P5 latency was longest during drowsiness, and shortest during activation while for left-ear stimulation the shortest latency occurred during relaxation. The amplitudes of Wave II and Wave VII were significantly smaller during drowsiness than during activation. Although the differences were below the level of clinical significance, the data indicate a modification in the characteristics of brainstem transmission as a function of concurrent activity in other brain areas.     

Chinese characters elicit face-like N170 inversion effects

Recognition of both faces and Chinese characters is commonly believed to rely on configural information. While faces typically exhibit behavioral and N170 inversion effects that differ from non-face stimuli (Rossion, Joyce, Cottrell, & Tarr, 2003), the current study examined whether a similar reliance on configural processing may result in similar inversion effects for faces and Chinese characters. Participants were engaged in an orientation judgment task (Experiment 1) and a one-back identity matching task (Experiment 2). Across two experiments, the N170 was delayed and enhanced in magnitude for upside-down faces and compound Chinese characters, compared to upright stimuli. The inversion effects for these two stimulus categories were bilateral for latency and right-lateralized for amplitudes. For simple Chinese characters, only the latency inversion effects were significant. Moreover, the size of the right-hemisphere inversion effects in N170 amplitude was larger for faces than Chinese characters. These findings show the N170 inversion effects from non-face stimuli closely parallel effects seen with faces. Face-like N170 inversion effects elicited by Chinese compound characters were attributed to the difficulty of part-whole integration as well as the disrupted regularity in relational information due to inversion. Hemispheric difference in Chinese character processing is also discussed.     

Chinese characters elicit face-like N170 inversion effects

Recognition of both faces and Chinese characters is commonly believed to rely on configural information. While faces typically exhibit behavioral and N170 inversion effects that differ from non-face stimuli (Rossion, Joyce, Cottrell, & Tarr, 2003), the current study examined whether a similar reliance on configural processing may result in similar inversion effects for faces and Chinese characters. Participants were engaged in an orientation judgment task (Experiment 1) and a one-back identity matching task (Experiment 2). Across two experiments, the N170 was delayed and enhanced in magnitude for upside-down faces and compound Chinese characters, compared to upright stimuli. The inversion effects for these two stimulus categories were bilateral for latency and right-lateralized for amplitudes. For simple Chinese characters, only the latency inversion effects were significant. Moreover, the size of the right-hemisphere inversion effects in N170 amplitude was larger for faces than Chinese characters. These findings show the N170 inversion effects from non-face stimuli closely parallel effects seen with faces. Face-like N170 inversion effects elicited by Chinese compound characters were attributed to the difficulty of part-whole integration as well as the disrupted regularity in relational information due to inversion. Hemispheric difference in Chinese character processing is also discussed.     

Simultaneous specification of amplitudes and directions of bimanual reversal movements

Intermanual interactions are modulated by task requirements in the course of motor preparation. In particular, amplitude coupling is strong when identical amplitudes are specified concurrently for the 2 hands but relaxed when different amplitudes are specified. Similarly, directional coupling is symmetric when symmetric directions are specified concurrently but turns to parallel when parallel directions are specified. Here, the author investigated whether the modulations of amplitude coupling and directional coupling in the course of motor preparation are independent or interact. Application of the timed-response procedure, which enables one to manipulate the time available for motor preparation, in 9 participants revealed a weakly interactive pattern. Directional coupling tended to be reduced when different rather than same amplitudes were specified concurrently, and amplitude coupling tended to be reduced when parallel rather than symmetric directions were specified concurrently. In general, interactive effects were also apparent in the rates at which directions and amplitudes were specified. Those observations are consistent with the notion that intermanual amplitude and direction interference are mediated by different but partially overlapping neural structures.     

Controlling velocity in rapid movements

It has often been reported that subjects prefer to use a strategy in which they vary movement velocity and peak amplitude in a linear fashion. In this study, control of velocity and amplitude in rapid reciprocating movements of the interphalangeal joint of the thumb was investigated by examining movement trajectories and patterns of activity in the extensor pollicis longus (EPL) and flexor pollicis longus (FPL) muscles. In controlling either amplitude or peak flexion velocity without constraint, subjects always used a strategy in which peak extension velocity and peak flexion velocity had strong linear correlations with movement amplitude. When they were required to keep either amplitude or peak flexion velocity fixed their movements were still biased toward a strategy in which peak velocity and movement amplitude covaried. It is suggested that the preferred strategy is related to a basic principle of scaling the magnitude and duration of a velocity profile in order to achieve different movement amplitudes.     

The roles of vibration amplitude and static force

Previous work (Verrillo, 1963, 1968) has shown that when measured as a change in absolute threshold, spatial summation occurs only at vibration frequencies above 40 Hz. The present study measured vibrotactile spatial summation at suprathreshold amplitudes. A matching task was used to investigate the effect of varying contactor size on sensory magnitude at three different vibration frequencies. Unlike the threshold data, increasing contactor size resulted in increases in sensory magnitude at 25 and 40 Hz as well as at 160 Hz. The amount of summation varied directly with amplitude for the two lower frequencies. In a second experiment, the effect of increasing static force, independent of contactor size, was investigated. The results indicated that the spatial summation effects noted in the first experiment may be due to increases in static force and not contactor area. The implications of these results for the concept of spatial summation and for the duplex mechanoreceptor hypothesis are discussed.     

Haptic shape perception from force and position signals varies with exploratory movement direction and the exploring finger

We investigated how exploratory movement influences signal integration in active touch. Participants judged the amplitude of a bump specified by redundant signals: When a finger slides across a bump, the finger’s position follows the bump’s geometry (position signal); simultaneously, it is exposed to patterns of forces depending on the gradient of the bump (force signal). We varied amplitudes specified by force signals independently of amplitudes specified by position signals. Amplitude judgment was a weighted linear function of the amplitudes specified by both signals, under different exploratory conditions. The force signal’s contribution to the judgment was higher when the participants explored with the index finger, as opposed to the thumb, and when they explored along a tangential axis, as opposed to a radial one (pivot ≌ shoulder joint). Furthermore, for tangential, as compared with radial, axis exploration, amplitude judgments were larger (and more accurate), and amplitude discrimination was better. We attribute these exploration-induced differences to biases in estimating bump amplitude from force signals. Given the choice, the participants preferred tangential explorations with the index finger—a behavior that resulted in good discrimination performance. A role for an active explorer, as well as biases that depend on exploration, should be taken into account when signal integration models are extended to active touch.     

Relativity of judgements about sound amplitude and the asymmetry of the same-different ROC

The problem of deciding whether two things are the same or different in magnitude can be solved by judging one magnitude relative to the other, or by making absolute judgements about the magnitude of each. The shape of the resulting receiver operating characteristic depends on which solution is adopted. In order to obtain empirical receiver operating characteristics, we therefore had subjects rate their confidence that two tone amplitudes were the same or different. Four subjects each made 500 ratings of three differences in amplitude. The asymmetry in the obtained characteristics indicated that subjects made relative rather than absolute judgements of the amplitudes, despite the fact that making absolute judgements would lead to better performance on the task.     

Period Duration of Physical and Im aginary Movement Sequences Affects Contralateral Amplitude Modulation

The hypothesis was tested that the strength of cross-manual effects of voluntary amplitude modulations in bimanual tasks increases when less preparation time is available during the execution of a sequence of movements. By means of the continuation procedure, various period durations (600, 800, 1200, and 1800 msec) of movement sequences were imposed. Subjects performed bimanual periodic arm movements on two digitizers: constant-amplitude movements (short or long) with the one hand, and movements of constant short or constant long amplitudes and movements of alternating short and long amplitudes with the other hand. Period-duration-dependent modulations of the amplitude were observed in movements of instructed constant amplitudes when the other hand performed alternating-amplitude movements, but not when the other hand performed constant-amplitude movements. Not only physical performance, but also the imaginary production of alternating-amplitude movements resulted in period-duration-dependent cross-manual effects, though reduced in size. The pattern of results is in agreement with a recently proposed two-level model of cross-manual effects according to which cross-talk can occur at the programming level as well as at the execution level.     

The effect of UCS intensity in classical and avoidance GSR conditioning

This study compared GSR avoidance and yoked-control conditioning procedures. Classical conditioning at two UCS intensities was followed by extinction and, two months later, by an avoidance session. Matching of Ss was based on GSR responsiveness and classical conditioning in the first session. The strong UCS led to more rapid reduction in CR latency (due to an increase in number of Ss responding) in the first session, and there was a tendency for maximum CR magnitude to occur in fewer trials with the strong UCS. No UCS-intensity difference in level of responding to the CS or UCS was found in the first session. A greater amount of spontaneous recovery in the second session was found in the strong UCS group. The avoidance and yoked control groups did not differ in CR magnitudes, latencies, or frequencies, nor in UCR magnitudes in the second session. They did differ significantly in the rate of decline in intertriai responses, the decline being more rapid in the avoidance condition.     

Multi-stepping saccadic sequences in humans

A number of paradigms are reported in which multi-stepping saccadic sequences (MSS) are reliably elicited in normal subjects. It was observed that MSS are consistently associated with a prolongation of the initial saccade latency. Further experiments show that this phenomenon is validated across a number of independent eye movement tasks. However, the probability of MSS occurring is reduced when temporal constraints are imposed on the latency of the response. An interpretation of these task-elicited MSS in terms of the neural mechanisms controlling voluntary saccades is proposed.