Visual and verbal coding in the interhemispheric transfer of information

A manual response was used to record a decision of ‘same’ or ‘differ’ on two visual signals which were presented simultaneously, either both to the same hemisphere or each to different hemispheres. The signals were drawn from the set of letters A, B, a, b. Eight subjects were required to match on the basis of the names of the letters (irrespective of whether they were capitals or lower case) and eight subjects were required to match on the basis of the visual identity of the signals.Reaction times were measured for ‘same’ and ‘differ’ decisions.This experiment extends a previous study by the same authors (Davis and Schmit 1971). The previous finding, that when two signals are presented each to different hemispheres, reaction times are shorter than when both are presented to the same hemisphere, was confirmed for both visual and name matching. New evidence is provided on the role of each hemisphere in the analysis and comparison of signals, on either a visual or a verbal basis, for ‘same’ and ‘differ’ decisions. A model to explain the results in terms of the different functions of the two hemispheres is proposed.     

Some evidence for a limited capacity parallel selfterminating process in simple visual search tasks.

An experiment was carried out in order to investigate the questions of exhaustive vs selfterminating and serial vs parallel processing in a simple visual search task. In the experiment, 1, 2 or 3 letters were placed on an imaginary circle round the fixation point. Two different letters were used, one of which was defined as the ‘signal’. Ss had to respond ‘yes’ when one or more signals were in the display, ‘no’ otherwise. The number of signals in the display was varied from ‘no signals’ to ‘all signals’.A decrease in latencies with increasing number of signals for a fixed number of elements presented was observed indicating a selfterminating search. A decrease in latencies with increasing number of elements when only signals were presented was taken as evidence for a parallel selfterminating process. A further analysis of the error data showed that a limited capacity system had to be assumed. It was shown that it was possible to construct the overall pattern of latencies over conditions from the error data obtained.     

Loudness and reaction time: I

It is widely assumed, based on Chocholle’s (1940) research, that stimuli that appear equal in loudness will generate the same reaction times. In Experiment 1, we first obtained equal-loudness functions for five stimulus frequencies at four different intensity levels. It was found that equal loudness produced equal RT at 80 phons and 60 phons, but not at 40 phons and 20 phons. It is likely that Chocholle obtained equivalence between loudness and RT at all intensity levels because of relay-click transients in his RT signals. One main conclusion drawn from Experiment 1 is that signal detection (in reaction time) and stimulus discrimination (in loudness estimation) require different perceptual processes. In the second phase of this investigation, the RT-intensity functions from six different experiments were used to generate scales of auditory intensity. Our analyses indicate that when the nonsensory or “residual” component is removed from auditory RT measures, the remaining sensory-detection component is inversely related to sound pressure according to a power function whose exponent is about — 3. The absolute value of this exponent is the same as the .3 exponent for loudness when interval-scaling procedures are used, and is one-half the size of the .6 exponent which is commonly assumed for loudness scaling.     

Division of attention between simultaneous and successive nonverbal signals varying in discriminability

Impaired performance indexed by accuracy usually accompanies the division of attention between simultaneous difficult signals. Presenting the signals successively reduces the impairment. Presenting easy signals eliminates it. Both variables crucial to these findings, relative time of onset and discriminability, were manipulated in the first experiment using a two-choice recognition paradigm involving bimodal signals. The results showed that, when a difficult signal was followed by two simultaneous easy ones, in a different modality from the first, performance was significantly worse on each than on the same signals presented alone. Simultaneous presentation of all three signals further increased the impairment for the difficult signal, but not for the easy ones. In the second experiment, the discriminability of the following signals was varied. The results showed, that when a difficult signal was followed by either two simultaneous easy signals, in a different modality from the first, or by two difficult ones, performance was significantly worse than on the same difficult signal presented alone. Further, when the preceding difficult signal was auditory, but not when it was visual, performance was better with easy following signals than with difficult ones. It is argued that an adequate account of the results from the two experiments requires the following assumptions concerning the processing of multiple signals: (1) a loss associated both with the acquisition and the storage of information, (2) preferential processing of visual signals over auditory ones. Proposals are made for the incorporation of both assumptions into a single model of divided attention.     

Social attention orienting integrates visual information from head and body orientation

Subjects were asked to detect visual, laterally presented reaction signals preceded by head-body cue stimuli in a spatial cueing task. A head rotated towards the reaction signal combined with a front view of a body resulted in shorter reaction times in comparison to the front view of a head and body. In contrast, a cue showing the head and body rotated towards the reaction signal did not result in such a facilitation in reaction times. The results suggest that the brain mechanisms involved in social attention orienting integrate ventrally processed visual information from the head and body orientation. A cue signaling that the other person, in his or her frame of reference, has an averted attention direction shifts the observer's own attention in the same direction.     

Driver's avoidance characteristics to hazardous situations: A driving simulator study

When analyzing the causes of an accident, it is critical to determine whether the driver could have prevented the accident. In previous studies on the reaction times of drivers, the definition and values of reaction times vary, so applying reaction time is difficult. In such analysis, the driver’s reaction time from perception is required to determine whether the driver could have prevented the accident, but past studies are difficult to utilize in accident analysis as reaction time measurements were taken after the occurrence of hazardous situations. In this study, 93 subjects from age groups ranging from 20 s to 40 s participated in an experiment inside a full-scale driving simulator, to determine reaction time values that can be practically applied to accident analysis. A total of 4 hazardous accident situations were reproduced, including driving over the centerline, pedestrian jaywalking, a vehicle cutting in, and intersection traffic signal violation. The Time-To-Collision (TTC) was 2.5 s and the driving speed was set to the common city road speed limits of 60 and 80 km/h. An eye tracker was used to determine the driver’s Saccade Latency (SL) during hazardous situations. Brake Reaction Time from Perception (BRT_P), Steer Reaction Time from Perception (SRT_P), and Driver Reaction Time from Perception (DRT_P) were derived, and the measurements were statistically analyzed to investigate differences by age group, gender, speed, and type of hazardous situation. Most participants were found to avoid collisions by braking first rather than steering for the presented hazardous situations, except for the cutting in situation. Also, to determine a reaction time that would cover most drivers, the 85th percentile of DRT_P was calculated. The 85th percentile of DRT_P was in the range of 0.550 – 0.800 s. Specifically for each hazardous situation, it was 0.650 s for driving over the centerline, 0.800 s for the pedestrian jaywalking, 0.660 s for cutting in, and 0.550 s for the intersection traffic signal violation. For all 4 hazardous situations combined, the 85th percentile of DRT_P was 0.646 s. The findings can be utilized to determine the driver’s likelihood of avoiding accidents when faced with similar hazardous situations.     

A critical path generalization of the additive factor method: Analysis of a stroop task

Sternberg's additive factor method was generalized to apply to tasks involving both serial and concurrent processing. The generalization is based on the critical path method of scheduling. The effects on reaction time of factors prolonging separate processes in a task are discussed; in general these effects are interactions of a simple form. Reaction times can be used to deduce, in part, the schedule of the mental processes in a task, including their order of execution. Bounds on process durations can be derived. Often there are redundant equations so the method can be easily rejected if it does not apply. A dual task experiment by Greenwald was analyzed. In the task subjects were presented with two stimuli and made a response to each under high and low compatibility conditions. Two bottlenecks in processing were located: (a) Subjects make only one decision at a time, in accordance with single channel theory, although the high compatibility condition may be an exception; (b) there is a mental process which takes longer when the stimuli conflict. The decisions about the two stimuli probably change places in the schedula when compatibility is changed.     

The role of auditory memory traces in attention to frequency

Three cued signal detection experiments demonstrated a role for auditory memory traces in frequency selectivity. The extent to which the cue predicted the signal frequency affected the size of the advantage for signals at the cue frequency over those at distant frequencies when the cue-signal gap was 10 sec but not when it was 1 sec. Detection of occasional signals presented at uncued frequencies was enhanced when they matched the frequency of cues from recent trials. With "relative" cues, which were usually followed by signals at the musical fifth above the cue frequency, performance on occasional signals at the cue frequency was enhanced relative to other unexpected frequencies. These results suggest that, regardless of the listener's expectations and intentions, the detectability of a signal is enhanced if its frequency matches an existing memory trace. One form of voluntary attention to frequency may involve maintaining traces that would otherwise slowly decay.     

Retinal and extraretinal information in movement perception: how to invert the Filehne illusion

During a pursuit eye movement made in darkness across a small stationary stimulus, the stimulus is perceived as moving in the opposite direction to the eyes. This so-called Filehne illusion is usually explained by assuming that during pursuit eye movements the extraretinal signal (which informs the visual system about eye velocity so that retinal image motion can be interpreted) falls short. A study is reported in which the concept of an extraretinal signal is replaced by the concept of a reference signal, which serves to inform the visual system about the velocity of the retinae in space. Reference signals are evoked in response to eye movements, but also in response to any stimulation that may yield a sensation of self-motion, because during self-motion the retinae also move in space. Optokinetic stimulation should therefore affect reference signal size. To test this prediction the Filehne illusion was investigated with stimuli of different optokinetic potentials. As predicted, with briefly presented stimuli (no optokinetic potential) the usual illusion always occurred. With longer stimulus presentation times the magnitude of the illusion was reduced when the spatial frequency of the stimulus was reduced (increased optokinetic potential). At very low spatial frequencies (strongest optokinetic potential) the illusion was inverted. The significance of the conclusion, that reference signal size increases with increasing optokinetic stimulus potential, is discussed. It appears to explain many visual illusions, such as the movement aftereffect and center-surround induced motion, and it may bridge the gap between direct Gibsonian and indirect inferential theories of motion perception.     

How do warnings influence cyclists' reaction to conflicts? Comparing acoustic and vibro-tactile warnings in different conflicts on a test track

An on-bike warning system has great potential to increase safety of cyclists. For an effective warning system, the implementation of warning signals is fundamental. However, more knowledge about the cyclist specific design of warnings and the influence of warnings on the cyclist is needed. To analyze the benefit of warnings in conflicts and the reaction pattern of cyclists we conducted a test-track experiment. We evaluated the data of 62 participants who were divided into three warning groups (between-subjects) and encountered different situations (within-subjects). The warning groups either received acoustic, vibro-tactile or no warnings. The situation variable consisted of three conflicts and two false warnings in the groups with warnings.We measured significantly shorter reaction times of persons who received acoustic and vibro-tactile warnings compared to the persons without warning. Furthermore, acoustic warnings led to shorter reaction times compared to vibro-tactile warnings. The reaction pattern was described by different bicycle dynamics variables. It was mostly influenced by the situation and rarely by the warning group. Based on the velocity curves and reaction times we identified learning effects describing how the warned participants adopted the warning system over the five situations.These findings indicate that a warning system offers great safety benefits to cyclists. Based on the current results, acoustic warnings are recommended when an urgent reaction is required.     

Divided attention: Evidence for coactivation with redundant signals

Many models of divided attention assume that signals presented on different channels produce separate activations, any one of which can initiate a response. According to these models, detection responses are especially fast when signals are presented on two channels at the same time because the system can detect a signal in either of two ways. Such models predict a testable relation among reaction time distributions for conditions in which a single signal is presented as compared with a condition in which two signals are presented, and this prediction is tested in two tasks. A bimodal detection task required a simple speeded response to either a visual or an auditory signal. A letter search task required a choice response depending on whether or not a two-letter display included the signal letter “A.” Data from both tasks are inconsistent with the prediction. When two signals are presented, responses are faster than separate-activation models can explain. The results favor “coactivation” models, in which signals presented on different channels contribute to a common pool of activation that initiates a response.     

Division of attention: Evidence for a between-trial component of impaired performance

Detection and recognition studies are reviewed, which show a dependency between errors on successive trials. They suggest the impairment accompanying the presentation of simultaneous signals may also involve a similar “between-trial” component. The hypothesis was tested using a two-choice recognition paradigm with bimodal signals. Dimensions presented simultaneously were interleaved on alternate trials with a single dimension presented alone. Interleaving two signals in the first experiment showed no effect on the following signal presented alone, compared to a control condition in which the signal always preceded itself. Interleaving four signals in the second experiment produced a significant impairment. Accounts of the results based on the length of the response interval, fluctuations of state variables such as arousal and decay of the memory trace are rejected. Accounts based on the impairment and set-size of preceding simultaneous signals are retained. Both suppose part of the impairment accompanying simultaneous signals to be a between-trial phenomenon. Implications of the results for work on divided-attention are considered and a method of experimental control proposed.     

Detection of auditory signals presented at random times: III

Reaction times to a pure tone in noise were measured. Throughout, the time from the warning signal to the reaction signal was exponentially distributed, and the signal was response terminated. Response criterion, signal intensity, and mean foreperiod wait were varied. A model that assumes a Poisson sensory transduction, a pulse-activated decision process, and an additive bounded residual process was tested. It was concluded that the assumed decision process was in error. Among the empirical results, the dependence of mean reaction time on signal waits was shown to depend largely on the average wait, not the actual one, and that this relationship between mean reaction time and average stimulus wait increased for strong signals and decreased for weak ones.     

Selective strategies in the assimilation of successively presented signals

It is found that performance in experiments on the psychological refractory period is highly affected by instructions. In the present experiment subjects were instructed either to handle the signals successively or to group them. Both instructions were obeyed. This seems to indicate that the human organism has various strategies available. Which strategy is actually applied is likely to depend on the structure of the experimental situation, and partly also, on momentary preference. This may explain the variety of results in the literature on this subject.

Finally, it is found that, when two signals are presented simultaneously, the total reaction time is considerably shorter if the signals are “grouped” than if they are “handled successively.” This difference disappears at interstimulus intervals of 0.2 sec. and 0.4 sec. The hypothesis is put forward, that the gain in time at the former case is due to simultaneous perceptual processing of the signals.     

A suppressing effect of response selection on immediate arousal in a choice reaction task

A clear conflict exists between experiments showing either additive or interactive effects of foreperiod duration and S-R compatibility on choice reaction time. It is hypothesized that in principle S-R compatibility and foreperiod duration have additive effects but that the effect of foreperiod duration is reduced in conditions where a signal is immediately arousing and where the S-R relations are highly compatible. In the case of low S-R compatibility the effect of immediate arousal is supposed to be ineffective.This hypothesis is tested and confirmed in an experiment in which the combined effects of foreperiod duration and S-R compatibility were studied with either loud (85 dBA) or weak (45 dBA) auditory signals. As predicted, additive effects were found in the latter case, while an interaction was observed with 85 dBA signals.     

Decisions concerning the rejected channel

It was thought that the physical aspects of auditory stimuli were possibly transmitted via separate pathways from those transmitting the verbal aspects. Three experiments were designed to test this hypothesis. In these experiments subjects had to perform a shadowing task and had to respond simultaneously on response keys to pips superimposed in either ear on verbal messages. The response to these pips was of increasing complexity, in that it was a simple reaction time which was measured in the first experiment, a choice reaction time in the second experiment and a more complex choice reaction time in the third experiment. Subjects were able to perform these tests although the increasing difficulty was reflected in longer reaction times and more errors. The reaction times to the pips presented to the ear which was not being shadowed were slower, and the errors, made to pips in both channels, were “false positives” rather than errors of omission. These results were taken as favouring the hypothesis.     

Some evidence for a selfterminating process in simple visual search tasks

Two experiments were conducted to investigate the unsettled question of whether the visual search process is selfterminating or exhaustive. In the experiments three letters were placed on an imaginary circle round the fixation point. Two different letters were used, one of which was defined as the ‘signal’. Ss had to respond ‘yes’ when one or more signals were in the display, ‘no’ otherwise. In both experiments the number of signals in the display was varied from 0 to 3.Decreasing latencies with increasing number of signals were observed in both experiments, indicating a selfterminating visual search. In experiment 1 a significant increase in latencies with increasing visual angle was found, in experiment 2 an increase in latency resulting from neighbouring contours. Both factors probably contribute to the slope of the function relating positive responses to display size and to the slope of the function relating negative responses to display size when stimuli are presented in linear arrays as in the experiment by Atkinson et al. (1969). As a result the slopes become more equal, falsely suggesting an exhaustive visual search process.     

Parametric coupling and generalized decoupling revealed by concurrent and successive isometric contractions of distal muscles

In two experiments we examined the hypothesis of transient parametric coupling during the specification of peak forces of isometric contractions produced by the left and right hand. In the first experiment participants had to produce bimanual contractions with same and different target forces as rapidly as possible in response to an auditory signal; target forces were cued visually with variable cueing intervals. At short cueing intervals reaction times were longer when different peak forces had to be specified than when same peak forces were cued, and this reaction-time difference declined as the cueing interval was increased. Independent of the cueing interval intermanual correlations of peak forces, rise times, and reaction times were smaller in conditions with different peak forces than in those with same peak forces. In the second experiment imperative signals for left-hand and right-hand contractions were separated in time. Target forces for the first response were cued with variable cueing intervals, while for the second response the cues were presented simultaneously with the second imperative signal. Reaction time of the second response was longer when target forces for the two successive responses were different rather than same, and this reaction-time difference declined when the delay of the second signal was increased as well as when the cueing interval for the first response became longer. These results are consistent with the hypothesis of a transient cross-talk between concurrent processes of peak-force specifications; in addition they indicate generalization of the decoupling required to specify different peak forces concurrently to the specification of temporal response characteristics and to processes of response initiation.     

Choice reaction times and the theory of intermittency in human performance

One visual signal, drawn from two equi-probable alternatives, was followed at a variable interval by a similar signal, also drawn from two equi-probable alternatives. The relationship between reaction time to the second signal and the interval between signals was studied under the following conditions: (1) Subjects were trained from the beginning to regard the first signal as irrelevant. (2) Subjects were asked to report on the nature of the first signal after they had responded to the second. The interval between signals was one of the five values, 50, 100, 150, 200, 250 millisec. In the regular interval situation the same interval was used over a block of 20 trials. In the random interval situation the values of the interval were randomly arranged, with equal frequency within each block of 20 trials.

The results showed: (1) In the random interval situation there was a definite disturbing effect of the first signal on the reaction time to the second, despite the fact that subjects were trained to disregard the first signal. However, the delays in reaction time were significant only at the shortest interval, 50 millisec. (2) In the regular interval situation this disturbing effect was not evident. (3) The additional requirement of having to report on the nature of the first signal produced no consistent increase in reaction time to the second signal. Some implications of these results for the conception of the human operator as a channel of limited capacity are discussed.     

Stimulus array onset as a preparatory signal in attentional selection

Warning signals enhance psychomotor performance by optimising preparation for the arrival of an event. Recent evidence, however, suggests that a warning signal can also disrupt attentional preparation by interfering with the process of preparing. It was hypothesised that a warning signal consisting of a change to the task-relevant items (array onset) may be more effective than a traditional warning signal consisting of the arrival, or removal, of a bar-cue which is independent of the task array. In three experiments array onset was a more effective warning signal than the bar-cue because reaction times were significantly faster without an increase in errors. In addition, an auditory warning signal resulted in faster reaction time than the bar-cue but in performance equivalent to that with an onset warning signal. Thus, the superiority of an auditory warning signal, reported by Davis and Green, was not found, when the interference of the visual warning signal with preparation was reduced. These results suggest that a visual warning signal consisting of a change to the stimulus array is more effective than an event independent from the stimulus array.