The lateralized readiness potential and response kinetics in response-time tasks.

Previous studies have found that the magnitude of the lateralized readiness potential (LRP) at the time of response initiation is constant across spontaneous variations in response time in both cued and uncued, speeded tasks. Other studies have found that the LRP is also unaffected by instructed changes in peak response force and time to peak force in cued, self-paced tasks, but that the LRP is sensitive to instructed changes in force gain rate in uncued, self-paced tasks. The present study examined the LRP in an uncued, speeded task as a function of response time and several measures of response kinetics. The magnitude of the LRP at the time of electromyographic onset was constant across spontaneous variations in all measures. The peak of the contingent negative variation did vary as a function of peak response force and integrated force to peak, but not response time. These findings support the idea that the LRP in speeded tasks is a selective, on-line index of the preparation associated with using a particular hand, and is not an index of the elements of motor programming that determine subsequent response kinetics.

Temporal stimulus-response compatibility.

The study of element-level stimulus-response compatibility (SRC) has predominantly focused on spatial and symbolic relationships and has involved measures of response time and (dichotomous) error rate. This article explores a new form of SRC that is observed when duration is the relevant feature of both the stimulus and the response, using a more extensive analysis of performance accuracy and variability. The results indicate that element-level SRC generalizes to situations involving time as the relevant dimension of stimuli and responses. Evidence of this was found in all of the extracted measures of performance; however, temporal SRC was shown to have independent effects on when and how accurately a response was made. Implications for SRC research are discussed.

Gastric myoelectrical and autonomic cardiac reactivity to laboratory stressors.

We evaluated the effects of two laboratory stressors (speech preparation and isometric handgrip) on gastric myoelectrical and autonomic cardiac activity, and the extent to which autonomic responses to these stressors and somatization predict reports of motion sickness during exposure to a rotating optokinetic drum. Both stressors prompted a decrease in preejection period (PEP) and respiratory sinus arrhythmia (RSA), and an increase in a dysrhythmic pattern of gastric myoelectrical activity, termed gastric tachyarrhythmia. Stressor-induced decreases in RSA and higher somatization scores predicted increased reports of motion sickness during drum rotation. These results demonstrate that laboratory stressors concurrently affect gastric myoelectrical activity and autonomic control of the heart, and that stressor-induced decreases in RSA and higher levels of somatization predict motion sickness susceptibility.

A questionnaire for the assessment of the multiple dimensions of motion sickness.

BACKGROUND: A limited number of attempts have been made to develop a questionnaire that assesses the experience of motion sickness. Further, many available questionnaires quantify motion sickness as a unidimensional construct. METHOD: Exploratory and confirmatory factor analyses of motion sickness descriptors were used to derive and verify four dimensions of motion sickness, which were defined as gastrointestinal, central, peripheral, and sopite-related. These dimensions of motion sickness were then used to construct a motion sickness assessment questionnaire (MSAQ) that was administered to individuals who were exposed to a rotating optokinetic drum. RESULTS: Total scores from the MSAQ correlated strongly with overall scores from the Pensacola Diagnostic Index (r = 0.81, p < 0.001) and the Nausea Profile (r = 0.92, p < 0.001). CONCLUSIONS: The MSAQ is a valid instrument for the assessment of motion sickness. In addition, the MSAQ may be used to assess motion sickness as a multidimensional rather than unidimensional construct.

Rate of force development and the lateralized readiness potential.

We examined the relationship between force and rate of force development aspects of movement dynamics and electroencephalogram motor components as reflected in the lateralized readiness potential (LRP). Using self-paced tasks, in Studies 1 and 3 we investigated whether differential speed and accuracy constraints in discrete and repetitive finger force production tasks influenced the LRP. These studies showed that speed tasks produced larger LRP than accuracy tasks regardless of whether the movement type was discrete or repetitive. In Studies 2 and 4 we studied four conditions with two levels of force and two levels of rate of force development. The largest LRPs were found with the greatest rate of force development. Overall, the four studies demonstrated that preparation for differential rates of force development is a major component reflected in the LRP.

Detecting the onset of the lateralized readiness potential: a comparison of available methods and procedures.

Studies that measure the onset of the lateralized readiness potential (LRP) could well provide researchers with important new data concerning the information-processing locus of experimental effects of interest. However, detecting the onset of the LRP has proved difficult. The present study used computer simulations involving both human and artificial data, and both stimulus- and response-locked effects, to compare a wide variety of techniques for detecting and estimating differences in the onset latency of the LRP. Across the two sets of simulations, different techniques were found to be the most accurate and reliable for the analysis of stimulus- and response-locked data. On the basis of these results, it is recommended that regression-based methods be used to analyze most LRP data.

Mechanisms of spatial attention revealed by hemispatial neglect.

We report performance by a patient, NG, with hemispatial neglect after nondominant stroke, in detecting briefly (200 msec) presented visual targets. NG's detection of targets (gaps in circles) was determined by the location of the target in the space in which stimuli appeared. Gaps on the neglected side of a circle at fixation were rarely detected when circles of uniform size were always presented at fixation. The same targets in the same location were detected far more often in blocks that also included targets presented on each side of the central circle, or in blocks that included larger target stimuli. In these blocks, the window of space in which stimuli appeared was larger, such that the target fell closer to the center of this "window". These results indicate that the spatial extent of attention, and of hemispatial neglect, can be modified on the the basis of expectations and task requirements.

Absence of coactivation in the motor component: evidence from psychophysiological measures of target detection.

Previous research examining response time has supported coactivation under certain conditions. Other research has found more forceful responses to redundant-target than to single-target displays, suggesting coactivation in the motor component. The authors tested for motor coactivation using response time, response force, and other psychophysiological measures. Experiments 1 and 2 showed that response force is determined by the number of stimuli, not the number of targets, when target-distractor discriminations are required. In Experiment 3, 1 stimulus was presented on each trial, and the number of target features was varied. The response time results showed that coactivation occurred somewhere in the information-processing system, but no evidence of motor coactivation was found using any psychophysiological measure. These data disconfirm the motor-coactivation hypothesis for tasks that require visual discriminations.

Response time and accuracy revisited: converging support for the interactive race model.

The interactive race model embodies 2 central claims: that divided attention is best described as a race between separately processed codes and that the 2 types of design contingency to which the model is sensitive affect different processing stages. Previous support for the model has come from a series of redundant-target tasks examining reaction time (RT) (J.T. Mordkoff & S. Yantis, 1991). We tested both central claims using near-threshold, accuracy tasks. This approach capitalizes on a known difference between RT and accuracy measures: that (in simple tasks) accuracy is sensitive only to perceptual manipulations, whereas RT is affected by both perceptual and postperceptual factors (J.L. Santee & H.E. Egeth, 1982). The results from 3 experiments provide converging support for the proposed loci of the 2 contingency-sensitive mechanisms within the interactive race model, as well as additional evidence concerning the differential sensitivities of RT and accuracy measures.

Redundancy gains and coactivation with two different targets: the problem of target preferences and the effects of display frequency.

When a visual display contains two targets, both of which require the same response, reaction times (RTs) are faster than when only one target appears. This effect has previously been obtained regardless of whether the redundant targets are the same or different in shape, and in at least one set of two-target experiments, the redundancy gains have been larger for different targets (Grice & Reed, 1992). Experiments with two different targets have also revealed violations of the race-model inequality, suggesting that redundant targets coactivate the response (Miller, 1982). The present paper reexamines both of these findings, because both appear to be inconsistent with the interactive race model (Mordkoff & Yantis, 1991). Experiment 1 shows that the race-model inequality is not violated when the experimental design is free of biased contingencies; Experiment 1 also provides evidence that target preferences may artifactually produce the RT advantage for different- over same-target trials. Experiment 2, however, shows that the race-model inequality is violated when the frequencies of single- and redundant-target displays are equated (without introducing any biased contingencies), implying that the interactive race model cannot account for the results of experiments involving more than one type of target. Alternative loci for coactivation are briefly discussed.

Dividing attention between color and shape: evidence of coactivation.

When attention is divided between spatially distinct objects, the time to detect a target decreases when two or more targets are present. This redundancy gain can be accounted for by an interactive race model (Mordkoff & Yantis, 1991) in which separate decisions are made about each object, but environmental contingencies among the objects can influence decision times. In the present study, we examined whether the model also accounts for performance when attention must be divided between stimulus attributes other than spatial location. Subjects made target-present responses when displays included a prespecified color, a prespecified letter, or both target features. The data violated the predictions of all separate-activations models, including the interactive race model. Two control experiments ruled out an alternative account based on task complexity. We conclude that coactivation occurs when target attributes from two separable dimensions are simultaneously present, but not when target attributes come from the same dimension. A modular hybrid of race and coactivation models is tentatively proposed.

Testing models of the redundant-signals effect: a warning concerning the combination-rule regression analysis.

The redundant-signals effect is the observed RT advantage for trials presenting two or more targets, as compared with trials with only one target. Two general classes of parallel-processing model have been proposed to explain this effect: race models (e.g., Raab, 1962) and coactivation models (e.g., Miller, 1982). Various distributional analyses have been used in work aimed at discriminating between these two model classes. The present study reexamined one of these tests--the combination-rule regression analysis based on variable-criterion theory (Grice, Canham, & Boroughs, 1984)--by applying it to the data from two sets of simulated experiments. One set of simulations assumed coactivation; the other set assumed an independent race on redundant-target trials. Nearly identical combination-rule values were observed in the two sets of simulations. This finding shows that the combination rule of variable-criterion theory does not discriminate between models capable of explaining the redundant-signals effect. The implications of this finding are briefly discussed.

An interactive race model of divided attention.

Two classes of models have been proposed to explain how redundant information extracted from separate sources comes to activate a single response. Each provides a fundamentally different account of why responses to redundant signals are typically faster than those to either signal alone (the redundant-signals effect). Independent race models assume that a race occurs between perceptual codes on independent channels and that only the winner activates the response. Coactivation models assume that there is some form of energy or activation-strength summation, with information being pooled across channels prior to decision. An intermediate class of models is introduced and a specific exemplar, the interactive race model, is tested in a series of redundant-target detection experiments. In particular, we examine the effects on performance of two types of contingency that have previously been overlooked as sources of task-relevant information. The results reveal that response times are significantly influenced by both interstimulus and stimulus-response contingencies. The interactive race model provides a natural account of these findings as well as several otherwise puzzling results in the divided-attention literature.

Detecting conjunctions of color and form in parallel.

Certain theories of visual attention assume that at least one processing stage must be serial when the target of search is defined as the conjunction of two or more separable features. To explain why conjunction-search response times do not always form linearly increasing functions of display size, recent versions of this general model have posited the existence of an early parallel process that guides the serial stage toward display elements that are likely targets. Other models have relaxed the seriality assumption, allowing for a limited number of parallel decisions. In the three experiments reported here, a redundant-target detection task was used with conjunctively defined targets and display sizes of two (Experiment 1), one or two (Experiment 2), and six (Experiment 3). In all three experiments, strong evidence for parallel processing was observed. The implications for models of elementary visual processes are discussed.