The relationship between latency of auditory evoked potentials,simple reaction time,and stimulus intensity

Summary The effects of loudness on the latency of evoked potentials and on simple reaction time were compared. It was found that both reaction time and the evoked-potential latency increases with decreasing stimulus intensity. However, different slopes of the curves were found. This is explained in terms of the arousal effect of loud auditory stimuli.     

Assimilation is due to one perceived whole and contrast is due to two perceived wholes

There is evidence that assimilation occurs when stimuli form one perceived whole. The assumption that a single internal event results in both a perceived whole and assimilation follows. There is also evidence that a transition from assimilation to contrast can occur. This assimilation should be due to one internal event, and this contrast is argued to be due to an interaction between the internal events for two perceived wholes. Another proposal is that at any one moment in time all stimuli result in an outcome that has a specific position on a continuum that ranges from one strong perceived whole to two interacting perceived wholes to two independent perceived wholes.     

The effects of stimulus numerosity,retinal location,and rod contrast on perceived duration of brief visual stimuli

The effects of manipulating three stimulus parameters were determined on a standard perceived duration task using 40- and 70-msec visual stimuli. In Experiment 1, it was found that perceived duration increased with increasing number of target dots but decreased as the area that contained the dots also increased. Experiment 2 examined the effect of varying the retinal location (0, 2, or 4 deg from fovea) of the target dot and found perceived target duration to increase with increasing eccentricity. In Experiment 3, the background luminance for a constant red target was varied so as to alter the scotopic contrast of the target. Perceived duration was minimal for the scotopically matched target and background conditions. The results of all three experiments were discussed in terms of important retinal—and even rod—contributions to tasks of perceived duration.     

Distortions of temporal integration and perceived order caused by the interplay between stimulus contrast and duration

Stimulus contrast and duration effects on visual temporal integration and order judgment were examined in a unified paradigm. Stimulus onset asynchrony was governed by the duration of the first stimulus in Experiment 1, and by the interstimulus interval in Experiment 2. In Experiment 1, integration and order uncertainty increased when a low contrast stimulus followed a high contrast stimulus, but only when the second stimulus was 20 or 30 ms. At 10 ms duration of the second stimulus, integration and uncertainty decreased. Temporal order judgments at all durations of the second stimulus were better for a low contrast stimulus following a high contrast one. By contrast, in Experiment 2, a low contrast stimulus following a high contrast stimulus consistently produced higher integration rates, order uncertainty, and lower order accuracy. Contrast and duration thus interacted, breaking correspondence between integration and order perception. The results are interpreted in a tentative conceptual framework.     

Visual adaptation to a spatial contrast enhances visual evoked potentials

The effects of adaptation to the visual contrast of a counterphase grating were studied with visual evoked potentials (VEPs). The spatial frequency of the grating was 4 cpd, and its temporal frequency was 4 or 12 Hz. Steady-state VEPs were analyzed through an FFT (fast Fourier transform) algorithm. In the first experiment, contrast thresholds rose strongly just after the end of adaptation and declined regularly over time. The VEPs recorded in the medio-occipital lead showed an initial decrease in amplitude after adaptation, followed by an enhancement well above the preadaptation level and then a return to that level. The paradoxical enhancement of the VEP was found at both high and low contrast in both the medio-occipital lead and the right temporal lead of a right-handed subject. The left temporal leads showed a VEP enhancement at high contrast and a decline at a low value.     

The relation between physical stimulus properties and the effect of foreperiod duration on reaction time

Seven subjects were used in an experiment on the relation between signal modality and the effect of foreperiod duration (EP) on RT. With visual signals the usually reported systematic increase of RT as a function of FP duration (1, 5 and 15 s) was confirmed; with auditory signals no difference was found between FP's of 1 and 5 s while the effect at 15 s was equivalent to that found at 5 s with the visual signal. The results suggest that besides factors such as time uncertainty the FP effect is also largely dependent on the arousing quality of the signal.     

Reaction time,evoked brain potentials,and psychometric g in the severely retarded

Measurements derived from reaction time (RT), movement time (MT), and an index of neural adaptability (NA) derived from averaged evoked potentials are significantly related to each other as well as to g factor scores extracted from a battery of 15 psychometric tests in a sample of 54 severely retarded adults. The RT-MT and NA variables show a shrunken multiple R of .64 (p < .001) with psychometric g.     

Confidence ill stimulus predictions and choice reaction time

In two choice reaction time (RT) experiments, a stimulus prediction and a confidence judgment in the prediction preceded each occurrence of one of two stimulus alternatives. Ss identified each stimulus presentation by pressing a left-hand or right-hand telegraph key. In Experiment I the source of the stimulus predictions and confidence estimates was varied between groups of 20 Ss. For each condition, RT to correctly predicted stimuli was an inverse function of prediction confidence. Following incorrectly predicted stimuli, RT was not reliably influenced by confidence when S gave both predictions and confidence judgments; but RT to incorrectly predicted stimuli was an increasing function of confidence when E verbalized the predictions and confidence estimates or when S predicted and E indicated confidence. In Experiment II Ss made predictions and the validity of Es confidence estimate was manipulated between Ss. When Es confidence was perfectly related to the probability of a correct prediction, choice RT to nonpredicted stimuli was inversely related to confidence. However, choice RT to nonpredicted stimuli was not affected by prediction confidence when Es judgments were random.     

Changes in middle latency auditory evoked potentials during meditation

In the present study of middle latency auditory evoked potentials during Brahmakumaris Raja Yoga meditation there was a decrease in the peak latency of the Na wave (a negative wave between 14 and 19 msec.) during meditation. Since the neural generator of this wave lies at the midbrain-thalamic level, from the results one can infer that the meditation reduces conduction time at this level.     

Judgments of the duration of visually marked empty time intervals: Linking perceived duration and sensitivity

The capability of subjects to categorize (as short or long) visually marked empty time intervals was investigated in three experiments. Two visual signals, located 18° to the left (L) and to the right (R) of a fixation point in the visual field, established four marking conditions, two unilaterally presented (L-L and R-R) and two bilaterally presented (L-R and R-L). In Experiments 1 and 2, the results show that discrimination is better with unilateral sequences than with bilateral sequences and that the perceived duration is longer with an L-R than with an R-L sequence. In addition, Experiment 2 shows that, in comparison with a condition in which Markers 1 and 2 remain identical for a complete session, varying the markers from trial to trial does not decrease discrimination. Also, Experiment 2 shows that discrimination is better when both visual markers are presented at fovea than it is in the unilateral conditions. Experiment 3 shows that bilateral intervals are perceived as being longer and are better discriminated than are intervals marked by an intermodal sequence (auditory-visual or visual-auditory). The general discussion reports the implications of having different perceived duration and sensitivity levels, in various marker-type conditions, for an internal-clock hypothesis. Some implications of these results for a lateralized-timer hypothesis are also discussed.