Reaction time to the onset and offset of electrocutaneous stimuli as a function of rise and decay time

Reaction times were obtained to the onset and offset of 70-cps electrocutaneous signals of five rise and decay times and five intensity levels. The results show that both onset and offset RTs increase linearly with increased rise and decay times. With fast rates of rise or decay, the onset produces faster RTs than the cessation of stimulation. The opposite effect is found when long rise and decay times are used. Interpretations of these results are given in terms of neural adaptation and accommodation.     

Effects of rate of signal rise and decay on reaction time to the onset and offset of acoustic stimuli

This study assessed the effects of variations in signal rise-decay time on response latencies to the onset and cessation of a 1,000-Hz tone. Onset and offset reactions were combined factorially with five rates of signal rise-decay (0.5, 5, 25, 100, and 250 msec) to produce a total of 10 experimental conditions. Offset RTs were significantly longer than onset RTs when the rise-decay time of the tone was 250 msec. Disparities in speed of reaction to tone onset and cessation were negligible at the remaining rates of signal rise-decay.     

Reaction time to the offset of brief auditory stimuli

An earlier investigator has found that the time at which the offset of a stimulus is perceived depends on the time of stimulusonset, rather than on the time of stimulus offset, for stimuli briefer than a critical duration of the order of 100 msec. In an attempt to determine whether this effect extends to reaction time (RT), we have determined RT to the offset of brief noise bursts. RT was found to be essentially constant as a function of stimulus duration. Thus, RT to stimulus offset appears not to be related to the time of perception of offset, as determined in the earlier investigations.     

Reaction time to tones in tonal backgrounds and a comparison of reaction time to signal onset and offset

In order to learn more about the processing of auditory information, simple reaction time (RT) measurements were made when subjects were asked to respond to tones presented against a tonal background. In the first experiment, a counterintuitive result was obtained: with two widely separated frequencies, 1,900 and 4,000 Hz, the presence of the background facilitated RT. In a second experiment, using two frequencies which were closer together (3,500 and 4,000 Hz), slowing of RT in the presence of the background was observed, as would be expected from the literature on auditory masking. A third experiment suggested that the information carried by signal offset is not an important factor in the facilitation observed with widely separated tones. In this experiment an unexpected result was found: subjects receiving offsets in their right ears responded significantly more slowly than did subjects receiving offsets in their left ears.     

Response latencies to the onset and offset of visual stimuli

Simple response times (RTs) are known to be slower to the offset of a visual stimulus than to its onset. This is called the onset advantage. In the first of four experiments, we discovered that a spurious onset advantage can be produced by the long persistence of P31 phosphor. In the remaining three experiments, we found that offset RTs were slower only when they were made in a context in which responses to the abrupt onset of some stimuli had to be suppressed. We tested this hypothesis of response suppression in two ways: (1) by mixing regular onset trials with other trials on which a response to an onset had to be suppressed, and (2) by ramping the emergence of "offset" stimuli over time, so that offsets were the only abrupt events in the display. In both cases, we found that the onset advantage depended critically on whether the responses were made in a context of response suppression. We conclude that the onset advantage is mediated not by sensory factors such as visible persistence, but by response programming factors that are strongly affected by contextual events.     

Response probability and response latency to threshold electrocutaneous stimuli

A comparison was made between two measures of somatosensory sensitivity, response probability, and reaction time to electrocutaneous constant current pulses of 350-microsec duration. The psychometric functions are steeper than those obtained for other sensory modalities. Similarly, the reaction-time/intensity functions are also steeper than those obtained in other modalities, i.e., larger decreases in reaction time as a function of small increases in stimulus intensity. Ss exposed to a broad stimulus range, including high intensities, yield psychometric and reaction time functions displaced into a higher intensity region than when they are exposed to a narrow low-intensity range of stimuli. The data are discussed in terms of a decision-theory model of reaction time.     

Reaction time to a second stimulus as a function of intensity of the first stimulus

Reaction time (RT) to the second of two stimuli presented in rapid succession was examined as a function of the intensity of the first stimulus (S₁). It was found that the delay in RT₂ was greater following a dim first stimulus than following a bright first stimulus. The magnitude of this increase corresponded to the difference in RTs to the two intensity levels of S₁. These results support the prediction of a single channel model of response selection. Examination of mean first RTs revealed a general elevation in latency of RT. However, since this increase was not influenced by the inter-stimulus interval (ISI) or by the intensity of the second stimulus (S₂), and since the same increase was found on “catch trials“ where no S₂ was presented, this increase is considered to be a function of change in set in the double response situation.     

Reaction time as a function of stimulus intensity for the monkey

Monkeys were trained to release a telegraph key in response to a visual or auditory stimulus. The latency of the key release response was measured for different stimulus intensities. In general, the relation between latency and intensity is inverse and exponential with greater variability of latency at the lower intensities. Some preliminary data involving differential reinforcement of short latencies are presented.     

Reaction time as a function of stimulus uncertainty on a single trial

In a discrete choice-reaction-time experiment, reaction times were measured between the onset of a light and the start of S’s pencil toward that light. The reaction time of unpracticed Ss, not aware that their first “practice” trial was being measured, increased as a linear function of stimulus uncertainty. Since this occurred without any prior experience, the effect must have been due to S’s set or expectancy regarding the nature of the future task, formed while the instructions for the task were being given.     

Reaction time to threat stimuli in panic disorder and social phobia

Two studies assessed response time among clinically anxious subjects and normal controls when presented with threat, positive and neutral stimuli under perceptual (lexical decision) and semantic (category decision) task conditions. In Study 1, panic disorder subjects' (n = 14) performance was compared to that of matched normal controls (n = 14) while in Study 2 social phobic subjects (n = 24) were compared to matched normal controls (n = 24). Relative to matched normal controls, panic disorder subjects but not social phobics tended to show greater slowing in performance on the more cognitively complex (category) task. A second finding, consistent across both studies was that, compared to the normal control groups, both panic and social phobic groups showed significantly slowed responses to threat words in both the perceptual and semantic tasks. Such findings are directly counter to the predictions of a mood congruence hypothesis. This apparent contradiction is resolved by a review of the literature which indicates that mood-related facilitation effects are obtained only in tasks which tap awareness of threat information rather than speed of response. It is suggested that while anxiety may produce enhanced awareness of threat, it may inhibit responsiveness to it. The results of these studies are seen as consistent with ethological theories of inhibited motoric responses under certain threat conditions. Furthermore, the findings suggest that caution is indicated in interpreting slowed reaction time to threat stimuli in tasks such as the Stroop color naming task as purely the result of attentional processes.     

Reaction time as a function of the intensity and probability of occurrence of vibrotactile signals

Three Ss made judgments of the presence or absence of a burst of 60-cps vibration onthe index fingertip.The probability of S’s reporting the presence of a signal was found to be influenced by signal probability and signal intensity. Mean reaction time for reporting the presence of a signal decreased as a function of signal intensity and signal probability whereas mean reaction time for reporting the absence of a signal increased as a function of signal intensity and signal probability. On trials where no signal was presented mean R T for reporting a signal decreased with increases in the signal probability whereas mean RT for reporting the absence of a signal increased with increases in signal probability. The results were interpreted as support for the hypothesis that S’s decision time was longer the closer on the sensory continuum a particular observation was to his criterion.     

Examining the time course of facilitation and inhibition with simultaneous onset and offset cues

The experiment conducted examined the effect of simultaneously presented onset and offset cues on the orienting of attention in the visual field. Subjects were presented with a display that consisted of four placeholder boxes around a central fixation point. An onset and an offset cue appeared simultaneously in two of the locations, and the other two locations provided a neutral baseline condition. Reaction times were measured in a simple target detection task with stimulus-onset asynchronies (SOAs) that ranged from 100 ms to 1,000 ms. As expected, the onset cue produced early facilitation and later occurring inhibition of return (IOR). The offset cue produced significant inhibition at all but the earliest SOA. These results suggest that simultaneously presented onset and offset cues both capture attention, but that attention is rapidly disengaged from the location of the offset cue, resulting in earlier occurring IOR. For the onset cues, attention is allocated for a longer period of time, producing the typical pattern of early facilitation and later occurring IOR. The differing time course of attention at each location may reflect separate facilitatory and inhibitory processes, and the priority given to the onset of a stimulus by the attentional system.