Locus of the redundant-signals effect in bimodal divided attention: A neurophysiological analysis

We reanalyzed the data from the study of Lamarre, Busby, and Spidalieri (1983). In that study, the activity of single neurons in area 4 of the motor cortex was recorded during a bimodal detection task in which a monkey (Macaca mulatta)had to respond as quickly as possible to a visual or an auditory signal or to both (redundant trials). Manual responses on redundant trials were speeded by the presence of both signals, as is typically found. The times between signal onsets and the first changes in neuronal activity were also speeded by redundant signals, but there was no difference between redundant-signals and single-signal trials in the time between the change in neuronal activity and movement onset. These results suggest that late motor processes are not speeded by redundant signals in bimodal detection tasks.     

Intersensory facilitation in the motor component?

Summary In the bimodal detection task the observer must respond as soon as a signal is presented in either of two modalities (e.g., a tone or a flash). A typical finding is a facilitation of reaction time for redundant signal trials, that is, when both signals are presented simultaneously or with a short delay. Models advanced for this effect imply either statistical facilitation (separate activation) or intersensory facilitation (coactivation). This paper reports a study investigating whether part of the facilitation can be accounted for by coactivation in the motor component. An analysis of the distributions of reaction time differences between left and right hand responses from a double response paradigm gave some evidence in favor of this hypothesis. In particular, our data suggest a u-shaped functional dependence of the amount of facilitation in the motor component on the interstimulus interval.     

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.     

Multisensory integration of vision and touch in nonspatial feature discrimination tasks

Multisensory integration of nonspatial features between vision and touch was investigated by examining the effects of redundant signals of visual and tactile inputs. In the present experiments, visual letter stimuli and/or tactile letter stimuli were presented, which participants were asked to identify as quickly as possible. The results of Experiment 1 demonstrated faster reaction times for bimodal stimuli than for unimodal stimuli (the redundant signals effect (RSE)). The RSE was due to coactivation of figural representations from the visual and tactile modalities. This coactivation did not occur for a simple stimulus detection task (Experiment 2) or for bimodal stimuli with the same semantic information but different physical stimulus features (Experiment 3). The findings suggest that the integration process might occur at a relatively early stage of object-identification prior to the decision level.     

The co-occurrence of multisensory competition and facilitation

Previous studies of multisensory integration have often stressed the beneficial effects that may arise when information concerning an event arrives via different sensory modalities at the same time, as, for example, exemplified by research on the redundant target effect (RTE). By contrast, studies of the Colavita visual dominance effect (e.g., [Colavita, F. B. (1974). Human sensory dominance. Perception & Psychophysics, 16, 409–412]) highlight the inhibitory consequences of the competition between signals presented simultaneously in different sensory modalities instead. Although both the RTE and the Colavita effect are thought to occur at early sensory levels and the stimulus conditions under which they are typically observed are very similar, the interplay between these two opposing behavioural phenomena (facilitation vs. competition) has yet to be addressed empirically. We hypothesized that the dissociation may reflect two of the fundamentally different ways in which humans can perceive concurrent auditory and visual stimuli. In Experiment 1, we demonstrated both multisensory facilitation (RTE) and the Colavita visual dominance effect using exactly the same audiovisual displays, by simply changing the task from a speeded detection task to a speeded modality discrimination task. Meanwhile, in Experiment 2, the participants exhibited multisensory facilitation when responding to visual targets and multisensory inhibition when responding to auditory targets while keeping the task constant. These results therefore indicate that both multisensory facilitation and inhibition can be demonstrated in reaction to the same bimodal event.     

Emotion affects action: Midcingulate cortex as a pivotal node of interaction between negative emotion and motor signals

Affective pictures drive the activity of brain networks and impact behavior. We showed previously that viewing unpleasant pictures interfered in the performance of a basic nonemotional visual detection task. In the present study, we employed functional magnetic resonance imaging to test the hypothesis that behavioral interference may result from the interaction between negatively valenced and motor-related signals in the brain. As in our previous study (Pereira et al., 2006), participants performed a simple target detection task that followed the presentation of unpleasant or neutral pictures. Our results revealed that an unpleasant emotional context modulated evoked responses in several regions engaged by the simple target detection task. In particular, the midcingulate cortex was recruited when participants performed target detection trials during the unpleasant context, and signal responses in this region closely mirrored the pattern of behavioral interference (as revealed via reaction time). Our findings suggest that the midcingulate cortex may be an important site for the interaction between negatively valenced signals and motor signals in the brain and that it may be involved in the implementation of defensive responses, such as freezing.     

Reduced response readiness delays stop signal inhibition

This study examines the effect of response readiness on the stopping of motor responses. Thirteen subjects performed a primary task requiring a speeded choice reaction on go trials and response inhibition on nogo trials. An occasional cue informed subjects that a nogo trial was imminent but left them uncertain about the number of go trials separating the cue and the upcoming nogo trial. This setup was meant to create test episodes of reduced response readiness (i.e., trial sequences initiated by the cue and terminated by the nogo signal) and control episodes, in which subjects were ready to execute a speeded choice reaction (i.e., trial sequences consisting only of go trials). During both episodes, a visual stop signal could occasionally and unpredictably follow go signal onset, instructing subjects to withhold their response to the go signal. Choice reactions on go trials were delayed during test episodes relative to control episodes. Most importantly, stop reactions were delayed, not facilitated, during test episodes compared to control episodes. These findings were taken to suggest that reduced readiness gives rise to more forceful responses that are then more difficult to inhibit.     

The problem of redundancy in movement control: The adaptive model theory approach

Summary The problem of redundancy in movement control is encountered when one attempts to answer the question: How does the central nervous system (CNS) determine the pattern of neural activity required in some 5,000,000 descending motor fibres to control only 100–150 biomechanical degrees of freedom of movement? Mathematically this is equivalent to solving a set of simultaneous equations with many more unknowns than equations. This system of equations is redundant because it has an infinite number of possible solutions. The problem is solved by the neuronal circuitry hypothesized in Adaptive Model Theory (AMT). According to AMT, the CNS includes neuronal circuitry able to compute and maintain adaptively the accuracy of internal models of the reciprocal multivariable relationships between outgoing motor commands and their resulting sensory consequences. To identify these input-output relationships by means of regression analysis, correlations between the input signals have to be taken into account. For example, if the inputs are perfectly correlated, the model reduces to a virtual one-input system. In general, the number of inputs modelled equals the number of degrees of freedom encoded by the signals; that is, the number of independently varying (orthogonal) signals. The adaptive modelling circuitry proposed in AMT automatically tunes itself to extract independently varying sensory and motor signals before computing the dynamic relationships between them. Inverse models are employed during response execution to translate movements preplanned as desired trajectories of these high-level sensory-feature signals into appropriately co-ordinated motor commands to send to the muscles. Since movement is preplanned in terms of a number of orthogonalized sensory-feature signals equal to the number of degrees of freedom in the desired response, the problem of redundancy is solved and the correlation or co-ordination between motor-command signals is automatically introduced by the adaptive models.     

选择性注意和分配性注意对多感觉整合的不同影响*

以简单图形为视觉刺激,以短纯音作为听觉刺激,通过指导被试注意不同通道（注意视觉、注意听觉、注意视听）以形成不同注意状态（选择性注意和分配性注意）,考察了注意对多感觉整合的影响,发现只有在分配性注意时被试对双通道目标的反应最快最准确。通过竞争模型分析发现,这种对双通道目标的加工优势源自于视听双通道刺激的整合。上述结果表明,只有在分配性注意状态下才会产生多感觉整合。     

Bimodal and trimodal multisensory enhancement: effects of stimulus onset and intensity on reaction time

Manual reaction times to visual, auditory, and tactile stimuli presented simultaneously, or with a delay, were measured to test for multisensory interaction effects in a simple detection task with redundant signals. Responses to trimodal stimulus combinations were faster than those to bimodal combinations, which in turn were faster than reactions to unimodal stimuli. Response enhancement increased with decreasing auditory and tactile stimulus intensity and was a U-shaped function of stimulus onset asynchrony. Distribution inequality tests indicated that the multisensory interaction effects were larger than predicted by separate activation models, including the difference between bimodal and trimodal response facilitation. The results are discussed with respect to previous findings in a focused attention task and are compared with multisensory integration rules observed in bimodal and trimodal superior colliculus neurons in the cat and monkey.     

Restraint and Cancellation: Multiple Inhibition Deficits in Attention Deficit Hyperactivity Disorder

We used variations of the stop signal task to study two components of motor response inhibition—the ability to withhold a strong response tendency (restraint) and the ability to cancel an ongoing action (cancellation)—in children with a diagnosis of attention deficit hyperactivity disorder (ADHD) and in non-ADHD controls of similar age (ages 7–14 years). The goal was to determine if restraint and cancellation were related and if both were deficient in ADHD. The stop signal task involved a choice reaction time task (go task) which required a rapid response. The demand for inhibitory control was invoked through the presentation of a stop signal on a subset of go trials which required that the ongoing response be suspended. The stop signal was presented either concurrently with the go signal (restraint version) or after a variable delay (cancellation version). In Study 1, we compared ADHD and control children on the cancellation version of the stop task; in Study 2, we compared ADHD and controls on the restraint version. In Study 3, a subset of ADHD and control participants completed both tasks so that we could examine convergence of these dimensions of inhibition. Compared to control participants, ADHD participants showed a deficit both in the ability to cancel and to restrain a speeded motor response. Performance on the restraint version was significantly correlated with performance on the cancellation version in controls, but not in ADHD participants. We conclude that ADHD is associated with deficits in both restraint and cancellation subcomponents of inhibition.     

The interplay of stop signal inhibition and inhibition of return

Inhibition of return (IOR) refers to slower responding to a stimulus that appears in the same rather than a different location as that of a preceding stimulus. The goal of the present study was to examine the relationship between IOR and stop signal inhibition. Participants were presented with two stimuli (S1 and S2) on each trial. On half of the trials (go trials), participants were required to make a speeded button-press response to report the location of S1; on the other half of trials (stop trials), they were required to cancel the response to S1, as indicated by the appearance of a stop signal at a variable delay (stop signal delay, SSD) after the appearance of S1. Success in cancelling an S1 response varied directly as a function of the SSD: The longer the delay, the more difficult it was for participants to cancel the prepared response. We examined the magnitude of IOR in the S2 reaction times as a function of whether participants made a correct go response to S1, made an erroneous non-cancelled response to S1, or successfully cancelled a response to S1. Our results indicated that the presentation of a stop signal increased the magnitude of IOR, even when the S1 response was not successfully cancelled. However, this was true only when the to-be-cancelled response involved the same effectors as the response used to reveal IOR. These results suggest that there may be a motor component to IOR that is sensitive to the same inhibitory processes that are used to cancel responses in a stop signal paradigm.     

Further evidence concerning scanning and sampling assumptions of visual detection models

Following extended training in a visual detection task, functions were determined for individual Ss relating latency of detection responses to number of redundant signal elements embedded in tachistoscopic displays of letters and to distance between signal elements. Latency proved invariant with respect to number of redundant signals and varied non-monotonically with distance. Of the several types of models considered in relation to previous studies, substantial support was forthcoming only for an independent stimulus sampling model. It is suggested that the detection method effects a relatively clear separation of the perceptual from the mnemonic aspects of the standard visual apprehension experiment, and that the sampling process may constitute only the first phase of a more general model which includes both parallel and serial information processing.     

Redundant visual signals boost saccade execution

The redundant signal effect (RSE) refers to the fact that human beings react more quickly to a pair of stimuli than to only one stimulus. In previous studies of the RSE in the oculomotor system, bimodal signals have been used as the goal of the saccade. In consistency with studies using manual response times (RTs), saccadic RTs have been shown to be shorter for redundant multimodal stimuli than for single unimodal stimuli. In the present experiments, we extended these findings by demonstrating an RSE in the saccadic system elicited only by unimodal visual stimuli. In addition, we found that shorter saccadic RTs were accompanied by an increased saccadic peak velocity. The present results are of relevance for neurophysiological models of saccade execution, since the boost of saccades was elicited by two visual transients (acting as a “go” signal) that were presented not at the goal of the saccade but at various other locations.     

Redundancy of noise elements and signals in visual detection of letters

Forced-choice detection was studied in relation to heterogeneity of noise letters and multiple signal letters within tachistoscopic displays. Curves plotting both probability and latency of correct detections vs number of redundant signals at different display sizes exhibit significant interactions with heterogeneity of the noise background, but do not differ as a function of similarity among redundant signals. Application of interactive and independent channels models indicated that noise redundancy operates to a major extent through effects of signal-noise confusability at the decision level, but may also involve perceptual interaction at the level of feature detectors.     

Moderating influences of hypnotic susceptibility on signal-detection task performance

This study investigated the differential influence of hypnotic susceptibility level on signal detection task (SDT) performance in waking and hypnotic conditions. As assessed by the Harvard Group Scale of Hypnotic Susceptibility, Form A (HGSHS: A) and the Stanford Hypnotic Susceptibility Scale, Form C (SHSS: C), 20 high (9–12), 20 medium (4–8), and 20 low (0–3) hypnotizables participated. In counterbalanced conditions of waking and hypnosis, Ss (Subjects) were given 36 signal detection trials, consisting of 12 strong signals, 12 weak signals, and 12 “no” signals. No differences were observed in the waking condition between low, medium, and high hypnotizables on strong and weak signal trials. In hypnosis, high hypnotizables exhibited significantly superior performance on the strong signal trials in comparison with low hypotizables, and performed significantly better on the weak signal trials than did the low and medium hypnotizables. Low and medium hypnotizables performed similarly in waking and hypnotic conditions, while high hypnotizables showed significant enhancements in performance for strong and weak signal trials during hypnosis. This research was supported, in part, by a grant from Fort Hays State University.     

Moderating influences of hypnotic susceptibility on signal-detection task performance

This study investigated the differential influence of hypnotic susceptibility level on signal detection task (SDT) performance in waking and hypnotic conditions. As assessed by the Harvard Group Scale of Hypnotic Susceptibility, Form A (HGSHS: A) and the Stanford Hypnotic Susceptibility Scale, Form C (SHSS: C), 20 high (9–12), 20 medium (4–8), and 20 low (0–3) hypnotizables participated. In counterbalanced conditions of waking and hypnosis, Ss (Subjects) were given 36 signal detection trials, consisting of 12 strong signals, 12 weak signals, and 12 “no” signals. No differences were observed in the waking condition between low, medium, and high hypnotizables on strong and weak signal trials. In hypnosis, high hypnotizables exhibited significantly superior performance on the strong signal trials in comparison with low hypotizables, and performed significantly better on the weak signal trials than did the low and medium hypnotizables. Low and medium hypnotizables performed similarly in waking and hypnotic conditions, while high hypnotizables showed significant enhancements in performance for strong and weak signal trials during hypnosis. This research was supported, in part, by a grant from Fort Hays State University.     

Facilitation of corticospinal excitability during motor imagery of wrist movement with visual or quantitative inspection of EMG activity

The present study investigated facilitation of corticospinal excitability during motor imagery of wrist movement with visual or quantitative inspection of background electromyographic (EMG) activity. Ten healthy participants imagined wrist extension from a first-person perspective in response to a start cue. Transcranial magnetic stimulation was delivered to the motor cortex 2 sec. after the start cue. EMG signals were recorded from the extensor carpi radialis muscle. Trials with background EMG activity were discarded based on visual inspection. Both motor-evoked potential (MEP) and background EMG amplitudes increased during motor imagery. The amount of increase in MEP amplitude was positively correlated with the amount of increase in background EMG amplitude during motor imagery. The statistically significant increase in MEP amplitude during motor imagery disappeared when the effect of muscle activity was statistically eliminated or after trials with background EMG activity were discarded based on strict quantitative criteria. Facilitation of corticospinal excitability during motor imagery of wrist movement depends partially on muscle activity. Discarding background EMG activity during motor imagery based on visual inspection is not sufficient to equalize background EMG amplitude between resting and motor imagery. Discarding trials with background EMG activity through strict quantitative criteria is useful to equalize background EMG amplitude between at rest and during motor imagery.     

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.     

Compatibility of precuing and of S-R mapping in choice reactions

This study investigates information processing elicited by precuing a subset of alternatives in a choice reaction task. The aim was to study the influence of some task variables on the effectiveness of precuing, in order to determine the locus of differential precuing effects, in either central decisional processing or in motor programming. Partial advance information (PAI) was given 300 msec in advance of the action signal and it indicated the subset from which the action signal would be chosen. Thus, precuing reduced the number of alternatives. The resulting decrease of reaction time (RT) was assessed under various levels of SR compatibility, response specificity and cue compatibility. Cue compatibility refers to the naturalness of the (spatial) relation between the cue signals and the stimulus-response pairs. This study shows that (a) precuing effectiveness is strongly affected by cue compatibility, and (b) cue compatibility should be viewed as a twofold concept: it refers to the naturalness of the relation of the cue signal, either with action signals or with responses.Experiment 1 compared a naming and a pointing task. Although in both tasks the cue signal was compatible with the cued action signals, the naming task had a lower level of SR compatibility and also a lower level of compatibility between the cue signal and responses. Precuing was highly effective when pointing towards the action signal, but hardly effective when naming ordinal positions. Experiments 2–4, using only a pointing task, showed a decrease of the precuing effect with a decrease of either type of cue compatibility, although cue compatibility with action signals was the strongest factor. Low SR compatibility further decreased the size of the precuing effect caused by low compatibility between cue and action signals. Differential precuing effects did not result from differences in response specificity (i.e., the lack of similarity among the cued responses). It is concluded that precuing and both types of cue compatibility affect the stage of response decision, while no evidence was found for effects on motor programming. Implications are discussed for movement precuing studies that rely on differential precuing effects to discover properties of motor programming.