Stage analysis of the reaction process using brain-evoked potentials and reaction time

Summary Motor processes partly determine reaction time (RT) in both choice reaction time and in binary classification tasks. These latter tasks are popular in cognitive psychology because the experimenter believes that he has kept the motor component simple and constant and therefore can attribute changes in RT to perceptual or cognitive processes. In this paper we used the P3 component of the event-related potential (ERP) as a time marker indicating the duration of perceptual and cognitive processes. The latency of this component is believed to reflect stimulus evaluation time independent of response selection and organization time.Two types of tasks were used: a choice-reaction time task and a binary classification task. Signal similarity and S-R compatibility additively affected RT, but only signal similarity affected P3 latency. The number of items in the positive set and response type affected both P3 latency and RT. Relative response frequency changed the bias in the cognitive evaluation of the stimulus, reflected in the latency of the P3 component, and affected RT only if the subjects preset their motor system (indexed by the late CNV). A model was presented which proposes that motor processes may partially overlap with the perceptual and cognitive evaluation of the stimulus. Both ERPs and RT are necessary tools in the study of the relative timing of these processes.     

On the rate of acquisition of visual information about space,time, and intensity

The temporal course of acquisition of visual information was mapped by measuring the speed and accuracy With which Ss could discriminate the position, intensity, or duration of a stimulus that was varied independently on these three binary dimensions. The speed-accuracy tradeoff was different for each of the three discrimination tasks, with performance substantially superior in the position discrimination task. In the intensity and duration discrimination tasks, there were systematic changes with RT in the relative influences of the three stimulus variables over the two alternative responses, suggesting .three phases of the corresponding perceptual processes: an initial dominance by position of the stimulus, a subsequent, joint influence by both intensity and duration, and finally an exclusive control by the correct dimension. The results demonstrate that Ss can selectively attend to various dimensions of the same stimulus, with concommitantly varying time constants. The perceptual processes being tapped by a discrimination task depend upon instructions and upon RT.     

Effects of variations in force and stimulus uncertainty on fractionated reaction time.

Previous research has shown that reaction time (RT) and premotor time varied as a function of force even in simple-RT paradigm. The present purpose was to examine whether stimulus uncertainty induced by catch trials would cause programming delay until after the signal to respond. Subjects were required to react and produce a designated peak force as soon as possible after a visual stimulus, with and without catch trials. Five different levels of force were 10, 30, 50, 70, and 90% of the maximum grip strength of subjects. Analysis showed that simple RT and premotor time changed as a function of force, regardless of whether catch trials were removed. These findings suggest that stimulus uncertainty is not a necessary condition for programming delay.     

The optimal experimental design for multiple alternatives perceptual search

Perceptual bias is inherent to all our senses, particularly in the form of visual illusions and aftereffects. However, many experiments measuring perceptual biases may be susceptible to nonperceptual factors, such as response bias and decision criteria. Here, we quantify how robust multiple alternative perceptual search (MAPS) is for disentangling estimates of perceptual biases from these confounding factors. First, our results show that while there are considerable response biases in our four-alternative forced-choice design, these are unrelated to perceptual biases estimates, and these response biases are not produced by the response modality (keyboard vs. mouse). We also show that perceptual bias estimates are reduced when feedback is given on each trial, likely due to feedback enabling observers to partially (and actively) correct for perceptual biases. However, this does not impact the reliability with which MAPS detects the presence of perceptual biases. Finally, our results show that MAPS can detect actual perceptual biases and is not a decisional bias towards choosing the target in the middle of the candidate stimulus distribution. In summary, researchers conducting a MAPS experiment should use a constant reference stimulus, but consider varying the mean of the candidate distribution. Ideally, they should not employ trial-wise feedback if the magnitude of perceptual biases is of interest.     

An investigation of the facilitation of simple auditory reaction time by predictable background stimuli

Two experiments explored a surprising result reported by Emmerich, Pitchford, and Becker (1976): Simple reaction time (RT) to an auditory stimulus can be facilitated by the presence of a tonal background (or masker). In the first experiment, simple RT to a tonal signal was investigated for a variety of background frequencies and loudness levels, and significant facilitation of RT was found for low levels of the background. In the second experiment, no evidence of facilitation was found when the background stimulus was a randomly varying narrow-band noise, although evidence for facilitation was again found with a constant tonal background.     

The boundaries of self face perception: Response time distributions,perceptual categories,and decision weighting

The current study uses an RT distribution analysis approach to examine the self-bias in face categorization. In two experiments we systematically manipulated the decision boundaries between the self, familiar, and unfamiliar others in face categorization tasks. For the first time in studies of self-categorization we estimated parameters from ex-Gaussian fits of reaction time distributions in order to capture the influence of different boundaries on the latency distribution of the categorization responses. The results showed that the distribution of responses to self faces was stable regardless of the face context and the task demands, and changes in context only shifted the response distribution in time. In contrast, varying the decisions with familiar and unfamiliar faces changed the shape of the RT distributions in addition to shifting RTs in time. The results indicate that, in contrast to our perception of familiar and unfamiliar faces of other people, self face perception forms a unique perceptual category unaffected by shifts in context and task demands.     

Impact of contingency manipulations on accessory stimulus effects

Accessory tone stimuli facilitate response performance despite being irrelevant for the current task. In order to investigate which processes are affected by accessory stimuli, we presented accessory tones in a simple response time (RT) task while varying the contingencies between accessory stimulation and either responses(Experiment 1) or stimulus conditions (Experiment 2). Accessory tones speeded up responding to a larger degree when they were conjointly presented within go compared with no-go trials. In contrast, contingency variation with stimulus conditions did not alter the impact of accessory stimuli. Additionally, accessory tones increased response force. Thus, we conclude that in simple RT tasks accessory tones influence response-related stages such as response selection and response execution rather than perceptual processes.     

Inhibition of return is not detected using illusory line motion

Inhibition of return (IOR) is the name that has been assigned to a response time (RT) delay to a stimulus presented at a recently stimulated spatial location. A commonly held explanation for the origins of IOR is that perceptual processing is inhibited and that this inhibition translates into slower RT. Three experiments with 10 subjects were used to directly test this perceptual explanation. The first two experiments assessed the level of perceptual facilitation present in the IOR paradigm using the frequency and latency of illusory line motion judgments. Contrary to the predictions of the perceptual view, the line motion and RT measures revealed only speeded processing at previously stimulated spatial locations. Experiment 3 required a simple detection response and used the same stimulus and timing parameters as those in Experiments 1 and 2. IOR was present, replicating the recent finding that judgments based on perceptual qualities of the stimulus do not demonstrate a RT delay, whereas simple detection tasks do show RT inhibition at previously stimulated locations. These findings are discussed in relation to a number of hypotheses about the origin of the RT delay.     

Enhancing and degrading visual stimuli

Several assembly language routines are described for use in perceptual identification experiments on the Apple Macintosh computer with MS-BASIC. These routines are in a machine language library that may be accessed from BASIC. No knowledge of assembly language is required to use the statements. In one method of perceptual identification, stimulus clarification, a mask is gradually removed to reveal the stimulus behind it. The other method, stimulus materialization, displays the stimulus on the screen in a piecemeal fashion. Data are reported from a demonstration experiment in which prior exposure to words enabled subjects to identify those words more easily under impoverished conditions.     

Exploring "fringe" consciousness: the subjective experience of perceptual fluency and its objective bases

Perceptual fluency is the subjective experience of ease with which an incoming stimulus is processed. Although perceptual fluency is assessed by speed of processing, it remains unclear how objective speed is related to subjective experiences of fluency. We present evidence that speed at different stages of the perceptual process contributes to perceptual fluency. In an experiment, figure-ground contrast influenced detection of briefly presented words, but not their identification at longer exposure durations. Conversely, font in which the word was written influenced identification, but not detection. Both contrast and font influenced subjective fluency. These findings suggest that speed of processing at different stages condensed into a unified subjective experience of perceptual fluency.     

Effects of auditory stimulus intensity on response force in simple, go/no-go, and choice RT tasks

In four experiments, increasing the intensities of both relevant and irrelevant auditory stimuli was found to increase response force (RF) in simple, go/no-go, and choice reaction time (RT) tasks. These results raise problems for models that localize the effects of auditory intensity on purely perceptual processes, indicating instead that intensity also affects motor output processes under many circumstances. In Experiment 1, simple RT, go/no-go, and choice RT tasks were compared, using the same stimuli for all tasks. Auditory stimulus intensity affected both RT and RF, and these effects were not modulated by task. In Experiments 2-4, an irrelevant auditory accessory stimulus accompanied a relevant visual stimulus, and the go/no-go and choice tasks were used. The intensity of the irrelevant auditory accessory stimulus was found to affect RT and RF, although the sizes of these effects depended somewhat on the temporal predictability of the accessory stimulus.     

Processing a hierarchy of stimulus pattern of 3 dimensions: a test of Navon's precedence hypothesis

The purpose of the experiments was to test generalizations derived from Navon's (1977) perceptual precedence hypothesis (global features are extracted earlier than local ones in feature analysis). Experiment 1 compared the identification of a level in hierarchically organized stimulus patterns (small letters forming larger letters on higher levels) between two- and three-level structures. Results showed an effect on reaction time (RT) of the imbedment of a level within a structure of sub- and superordinated levels: The same level will be identified more quickly if it is the local level of a two-level letter than if it is the medium level of a three-level letter. This effect can be explained by the loss of the most easily noticed privileged structural position. This result and the observed longest RT for identifying the middle level in a three-level letter contradict expectations derived from Navon's (1977) hypothesis of perceptual precedence. Experiment 2 tested a variant of the precedence hypothesis by Kinchla and Wolfe (1979). On the basis of this hypothesis it can be expected that RT for identification of the middle level should converge toward those for the other levels if the middle level is presented at about 2 degrees. This hypothesis could not be confirmed. Results are discussed in the context of a proposed attentional explanation. This explanation suggests that a structural level is noticed more easily if it segregates perceptually from the other levels. In this respect, the global level usually but not necessarily has an advantage.     

Reaction time and movement time measured in a key-press and a key-release condition.

Reaction time (RT) and movement time (MT) are measured in two conditions, a key-press and a key-release condition. The latter makes a greater demand on perceptual feedback than the former. RT increases in the key-release condition and a fraction of MT denoted key-press time (KT) decreases in the key-press condition. It is argued that KT of a response button in the simple reaction-time experiment may serve as a proper measure of the motor component. The foreperiod prior to onset of the reacting stimulus affects RT, KT, and MT, suggesting that preparatory set or expectancy influences both the perceptual and motor components of simple human performance. The results indicate that the relation of RT and MT depends upon methodological conditions.     

Spatial distribution of visual attention: Perceptual sensitivity and response latency

Studies of the spatial distribution of visual attention have shown that attentional facilitation monotonically decreases in a graded fashion with increasing distance from an attended location. However, reaction time (RT) measures have typically shown broader gradients than have signal detection (SD) measures of perceptual sensitivity. It is not clear whether these differences have arisen because the stages of information processing indexed by RT measures are different from those indexed by SD measures, or whether these differences are due to methodological confounds in the SD studies. In the present set of experiments, the spatial distribution of attention was studied by using a luminance detection task in an endogenous cuing paradigm that was designed to permit accurate calculations of SD and RT measures for targets at cued and uncued locations. Subjects made target-present/absent decisions at one of six possible cued or uncued upper visual hemifield locations on each trial. The results from three experiments suggest that the differences between broad and focal attentional distributions are not the result of different stages of information processing indexed by RT measures as opposed to SD measures. Rather, the differing distributions appear to reflect variations in attentional allocation strategies induced by the perceptual requirements typical of RT paradigms as opposed to SD paradigms. These findings support numerous prior studies showing that spatial attention affects perceptual sensitivity and that the strategic allocation of attention is a highly flexible process.     

Dual payoff band control of reaction time

The location of a S’s simple reaction time (RT) distribution can be controlled by differential reinforcement of RTs that fall within specified temporal limits called a payoff band. Both humans and monkeys can gradually shift the location of a single RT distribution over hundreds of milliseconds in accord with changing payoff band requirements. This study establishes that trained human Ss can also accurately shift theft response latencies back and forth between two different RT distributions when the payoff band is changed from trial to trial. On each trial, the color of the warning stimulus indicated which of two payoff bands would be in effect when the S reacted to a light flashed 1,500 msec later. The RT distributions produced under the condition of random trial-to-trial switching between two payoff bands were the same as the low-variability RT distributions produced when only one payoff band was in effect over a long series of trials.     

Identification and bisection of temporal durations and tone frequencies: common models for temporal and nontemporal stimuli

Two experiments examined identification and bisection of tones varying in temporal duration (Experiment 1) or frequency (Experiment 2). Absolute identification of both durations and frequencies was influenced by prior stimuli and by stimulus distribution. Stimulus distribution influenced bisection for both stimulus types consistently, with more positively skewed distributions producing lower bisection points. The effect of distribution was greater when the ratio of the largest to smallest stimulus magnitude was greater. A simple mathematical model, temporal range frequency theory, was applied. It is concluded that (a) similar principles describe identification of temporal durations and other stimulus dimensions and (b) temporal bisection point shifts can be understood in terms of psychophysical principles independently developed in nontemporal domains, such as A. Parducci's (1965) range frequency theory.     

反馈延迟与掩蔽类型对知觉类别学习的影响

通过两个实验探讨反馈延迟与掩蔽类型对知觉类别学习的影响。实验1光栅掩蔽条件下,采用2（类别结构：基于规则vs.信息整合）×2（延迟反馈：500vs.3000ms）被试间实验设计,实验2采用同样的实验设计,保持延迟反馈时间不变,但改掩蔽类型为黑屏掩蔽。结果发现：（1）光栅掩蔽条件下,反馈延迟削弱信息整合类别结构的成绩,不影响基于规则类别学习,内隐外显类别结构之间存在分离效应。（2）黑屏掩蔽条件下,信息整合与基于规则类别结构的成绩均不受到延迟反馈的影响,分离效应消失。实验说明“无关因素”掩蔽影响知觉类别学习,知觉噪音与标准噪音在反馈延迟影响知觉类别学习中起到重要作用,COVIS模型理论关于延迟反馈时间影响知觉类别学习的解释具有局限性。     

How much processing do nonattended stimuli receive? Apparently very little, but...

The early versus late selection issue in attention models was examined by means of a new methodology. Through cues or precues, attention was directed to one location of a multistimulus visual display and, while attention was so engaged, the identity of a stimulus located at a different position in the display was changed. By varying the time after display onset before the stimulus was changed, we controlled the preview time that the original stimulus was represented on the retina. Then, using a marker cue, we directed the subject's attention to the location of the changed stimulus. The subject's response was a timed discrimination between two possible target letters. The data of main interest was the effect of preview time upon the subject's latency in identifying the new target that appeared in the changed location. We found that the preview time of the original stimulus, before RT was affected to the new target, depended upon whether the original stimulus was a neutral (noise) letter or whether it was the alternative target. When the original stimulus was a noise letter, RTs to the new target were just as fast as those obtained in the control condition in which the target was present throughout the preview interval and did not change its identity. Significant effects upon RT were obtained at preview times of 83 msec when the original stimulus was one of the targets that changed to the alternative target. Preview times also varied as a function of precuing. Preview times were correspondingly shortened when the first cue occurred 50 msec before display onset, thus providing an extra 50 msec for attention to be directed to the first display location. The results were interpreted in terms of two separate information-processing systems in the human: an automatic system and an attentional system. Even though a stimulus may have been automatically processed, when the attention system is directed to that stimulus, processing starts at the beginning again.     

Attentional zooming and the global-dominance phenomenon: Effects of level-specific cueing and abrupt visual onset

Summary In four experiments level-specific cueing of hierarchically structured stimuli was used to test the hypothesis that valid cues can reduce the global-dominance phenomenon. Compound stimuli (Experiments 1 and 2) or simple geometric forms (Experiments 3 and 4) were presented with different SOAs after a valid, an invalid, or a neutral level-specific cue (cue validity 80%). Costs for invalid cues and benefits for valid cues were produced in all experiments. However, a reduction of the global-local RT difference to about zero was achieved only after the reduction of the abrupt visual onset accompanying stimulus presentation in Experiments 2 (with compound stimuli) and 4 (with simple geometric forms). In addition, there was no longer the typical asymmetric-interference pattern (i. e., features of the global level interfere with local identification, but not vice versa) that was one of Navon's (1977) main arguments for assuming a perceptual precedence. It is concluded that the RT that is longer for local than for global identifications is produced by the time needed to refocus visual attention intentionally from the global level, which is focussed at first unintentionally, to the local level.     

The role of attention in the facilitation effect and another "inhibition of return"

The present study investigated how anticipation of a target's appearance affects human attention to gaze cues provided by a schematic face. Subjects in a 'catch' group received a high number of 'catch' trials, in which no target stimulus appeared. Subjects in the control group did not receive any catch trials. As in previous studies, both groups showed a facilitation effect to the cued location during shorter stimulus onset asynchrony (SOA). In both groups, an analysis of eye movements confirmed that subjects' eyes remained on the fixation point, ruling out the possibility that the facilitation effect was due to shifting eye movements (saccades) as opposed to a shift in covert attention. But while the control group's response time (RT) decreased as SOA increased, the catch group's RT had a U-shaped pattern and the facilitation effect to the cued location was reversed at the longest SOA (1005 ms). These results suggest that subjects in the catch group disengaged their attention during long SOAs because they expected the trial to be a catch trial. This disengagement of attention during long SOAs results in a delay before attention could be re-focused to the previous location regardless of the cue validity ["IOR (inhibition of return)"-like-phenomenon]. Unlike the conventional IOR, we suggest that this "IOR"-like phenomenon caused by an unpredictive central gaze cue is likely to be mediated by an endogenous mechanism.