Spontaneous decay of response-code activation

Summary Two experiments investigated whether theTwo experiments investigated whether the Simon effect (i. e.., faster responses to spatially corresponding than to noncorresponding stimuli, with stimulus location being irrelevant) is affected by the frequency of noncorrespondence trials. Stimulus discriminability (Experiment 1) and immediate or delayed stimulus formation (Experiment 2) was varied in order to manipulate the temporal relationship between coding of the relevant stimulus information and of stimulus location. As was expected, the Simon effect decreased from high to low discriminability and from immediate- to delayed-stimulus formation. This is consistent with the notion of a gradual decay of location-induced response-code activation. Moreover, the Simon effect decreased with increasing frequency of noncorrespondence trials and was even reversed with higher frequency. This demonstrates strategic preparation of stimulus processing and/or response selection based on irrelevant location information. However, frequency did not modify the interaction between S-R correspondence and stimulus discriminability or stimulus formation, this suggesting that code decay is not a result of a strategy, but an automatic process.     

Developmental differences in response processing

Three age groups (kindergartners, fourth graders, and adults) were compared in their processing of response decisions in a two-choice reaction time task. Manipulation of spatial stimulus-response compatibility resulted in age-related differential effects on reaction time performance. For the younger children, selecting the appropriate response for an incompatibly paired stimulus light required proportionately longer processing time than for older subjects. Similar results were not found for performance under varying levels of response discriminability.     

Effects of stimulus-response correspondence and verbal expectancy on choice reaction time.

The effects of S-R correspondence, verbal prediction, and stimulus discriminability were examined in a discrete, two-choice reaction-time task. Correctness of prediction and S-R correspondence were significant main effects. In addition, responses were significantly faster for correct predictions on noncorresponding trials than for incorrect predictions on corresponding trials. This latter finding indicates that an expectancy mechanism can partially offset the negative effect of spatial S-R noncorrespondence on absolute magnitude of choice reaction time.     

The additivity of stimulus-response compatibility with perceptual and motor factors in a visual choice reaction time task

One hundred and four participants performed a two-choice reaction time task requiring button-press responses to visual stimuli. Two levels of stimulus-response compatibility were factorially combined with two levels of stimulus discriminability and two levels of response repertoire. Results showed that the effects of these three variables were additive both in terms of mean reaction time as in terms of reaction time variances. The implication of this outcome is discussed in terms of the underlying information processing stage structure.     

Reaction time distribution analysis of spatial correspondence effects

Since 1994, group reaction time (RT) distribution analyses of spatial correspondence effects have been used to evaluate the dynamics of the spatial Simon effect, a benefit of correspondence of stimulus location information with response location for tasks in which stimulus location is irrelevant. We review the history and justification for analyzing group RT distributions and clarify which conditions result in the Simon effect decreasing across the distribution and which lead to flat or increasing functions. Although the standard left-right Simon effect typically yields a function for which the effect decreases as RT increases, in most other task variations, the Simon effect remains stable or increases across the RT distribution. Studies that have used other means of evaluating the temporal dynamics of the Simon effect provide converging evidence that the changes in the Simon effect across the distribution are due mainly to temporal activation properties, an issue that has been a matter of some dispute.     

Localizing practice effects in dual-task performance

Practice effects on dual-task processing are of interest in current research because they may reveal the scope and limits of parallel task processing. Here we used onsets of the lateralized readiness potential (LRP), a time marker for the termination of response selection, to assess processing changes after five consecutive dual-task sessions with three stimulus onset asynchronies (SOAs) and priority on Task 1. Practice reduced reaction times in both tasks and the interference between tasks. As indicated by the LRP, the reduction of dual-task costs can be explained most parsimoniously by a shortening of the temporal demands of central bottleneck stages, without assuming parallel processing. However, the LRP also revealed a hitherto unreported early activation over the parietal scalp after practice in the short SOA condition, possibly indicating the isolation of stimulus–response translation from other central processing stages. In addition, further evidence was obtained from the LRP for a late motoric bottleneck, which is robust against practice.     

The relationship between stimulus processing and response selection in the Simon task: Evidence for a temporal overlap

Summary As is indicated by the Simon effect, choice reactions can be carried out faster when the response corresponds spatially to the stimulus, even if the stimulus location is irrelevant to the task. In Experiments 1–4 the relationships between the Simon effect and stimulus eccentricity, signal quality, and signal-background contrast are investigated. The Simon effect was found to interact with all of these factors, at least when manipulated blockwise. These results are at odds with previous results and are difficult to interpret from an additive-factor-method view. An alternative interpretation is suggested that attributes the results to the temporal relationship between the processing of the relevant stimulus information and stimulus location. The assumption is that a decrease in the Simon effect is caused by every experimental manipulation that markedly increases the temporal distance between the coding of the relevant stimulus information and that of the irrelevant stimulus location. This assumption was tested in Experiment 5 in a more direct way. The stimuli were built up on a screen over time, so that the temporal distance between the presence of location and identity information could be controlled experimentally. The results provide further support for a temporal-delay interpretation of interactions between irrelevant stimulus-response correspondence and factors that affect early stages of information processing.     

The effects of number of sample stimuli and number of choices in a detection task on measures of discriminability

Six pigeons were trained on a conditional discrimination task involving the discrimination of various intensities of yellow light. The research asked whether stimulus—response discriminability measures between any pair of stimuli would remain constant when a third or fourth sample and reinforced response were added. The numbers of different sample stimuli presented and different responses reinforced were two (Part 1), three (Parts 2 and 4), and four (Part 3). Across conditions within parts, the ratios of reinforcers obtainable for correct responses were varied over at least five levels. In Part 5, the numbers of sample stimuli and reinforced responses were varied among two, three, and four, and the reinforcer ratio between consecutive remaining samples was constant at 2:1. It was found that once a particular response had been reinforced, subjects continued to emit that response when the conditional stimulus for that response was no longer presented. Data analysis using a generalization-based detection model indicated that this model was able to describe the data effectively. Four findings were in accord with the theory. First, estimates of stimulus—response discriminability usually decreased as the arranged physical disparity between the sample stimuli decreased. Second, stimulus—response discriminability measures were independent of response—reinforcer discriminability measures, preserving parameter invariance between these measures. Third, stimulus—response discriminability measures for constant pairs of conditional stimuli did not change systematically as conditional stimulus—response alternatives were added. Fourth, log stimulus—response discriminability values between physically adjacent conditional stimuli summed to values that were not significantly different from estimates of the discriminability values for conditional stimuli that were spaced further apart.     

Reflexive Attention Modulates Processing of Visual Stimuli in Human Extrastriate Cortex

Attention can be oriented reflexively to a location in space by an abrupt change in the visual scene. In the present study, we investigated the consequences of reflexive attention on the neural processing of visual stimuli. The findings show that reflexively oriented attention produces modulations in early sensory analysis at the same extrastriate neural locus as the earliest effects of voluntarily focused attention. In addition, stimulus processing was found to be enhanced at later stages of analysis, which reflect stimulus relevance. As is the case with behavioral measures of reflexive attention, these physiological enhancement effects are rapidly engaged but short-lived. As time passes between the initial attention-capturing event and subsequent stimuli, the extrastriate effect reverses, and the enhancement of higher order processing subsides. These findings indicate that reflexive attention is able to affect perceptions of the visual world by modulating neural processing as early as extrastriate visual cortex.     

A random-walk model of accuracy and reaction time applied to three experiments on pigeon visual discrimination

A random-walk model of visual discrimination is described and applied to reaction time (RT) distributions from three discrete-trial experiments with pigeons. Experiment 1 was a two-choice hue discrimination task with multiple hues. Choice percentages changed with hue discriminability; RTs were shortest for the least and most discriminable stimuli. Experiments 2 and 3 used go/no-go hue discriminations. Blocks of sessions differed in reward probability associated with a variable red stimulus in Experiment 2 and with a constant green stimulus in Experiment 3. Changes in hue had a large effect on response percentage and a small effect on RT; changes in reward shifted RT distributions on the time axis. The "random-walk, pigeon" model applied to these data is closely related to Ratcliff's diffusion model (Ratcliff, 1978; Ratcliff & Rouder, 1998). Simulations showed that stimulus discriminability affected the speed with which evidence accumulated toward a response threshold, in line with comparable effects in human subjects. Reward probability affected bias, modeled as the amount of evidence needed to reach one threshold rather than the other. The effects of reward probability are novel, and their isolation from stimulus effects within the decision process can guide development of a broader model of discrimination.     

Differential dynamics of spatial and non-spatial stimulus-response compatibility effects: a dual task LRP study

Choice reaction times are shorter when stimulus and response features are compatible rather than incompatible. Recent studies revealed that spatial compatibility effects in Simon tasks are strongly attenuated when there is temporal overlap with a different high-priority task. In contrast, non-spatial variants of the Simon task appear to be unaffected by task overlap. The present study used the lateralized readiness potential (LRP) within a dual task design to elucidate the dynamics underlying these differential effects for a color and a spatial variant of the Simon task. In the color version there was no sign of early response priming by irrelevant stimulus features in the LRP. The color compatibility effect was independent of task overlap and reflected in the LRP onset latency. In contrast, in the spatial version, priming by irrelevant stimulus location showed up and was mirrored by early LRP activation. Response priming and the corresponding Simon effect, however, were present only in case of little temporal overlap with the primary task. The absence of spatial compatibility effects at strong temporal overlap suggests that response conflicts due to stimulus-related priming depend on the availability of processing resources.     

The enhanced Simon effect for older adults is reduced when the irrelevant location information is conveyed by an accessory stimulus

The Simon effect, better performance when irrelevant stimulus location corresponds with the response location than when it does not, typically is larger for older than younger adults. However, Simon and Pouraghabagher [Simon, R. J., & Pouraghabagher, A. R. (1978). The effect of aging on the stages of processing in a choice reaction time task. Journal of Gerontology, 33, 553-561] found no age difference using an accessory-stimulus Simon task in which the relevant dimension was the color of a visual stimulus and the irrelevant dimension the location of a tone. Experiment 1 confirmed that older adults show a larger Simon effect than younger adults for the visual Simon task and that this age-related deficit is reduced or eliminated for the auditory-accessory task. Experiment 2 provided evidence suggesting that a small part of the age-related deficit in the visual Simon task is due to having to code the location of the relevant stimulus, but Experiment 3 showed that the majority of the deficit is due to the relevant and irrelevant information being conveyed by the same stimulus. Reaction-time distribution analyses show similar functions for younger and older adults, suggesting that the time course of activation is similar for both age groups.     

Precueing spatial S-R correspondence: is there regulation of expected response conflict?

Four experiments investigated the ability to prepare for the level of forthcoming stimulus-response correspondence in choice-response tasks. In a Simon task, participants responded to the color of spatially variable stimuli with spatially variable responses. Participants were given advance information about whether a forthcoming stimulus-response event would be spatially corresponding, neutral, or spatially noncorresponding. Reliable cues decreased reaction times (RTs) in the corresponding conditions of 2- and 3-choice tasks, decreased RTs in noncorresponding conditions of a 2-choice task but not in a 3-choice task, and left RTs in neutral conditions unaffected. The pattern of results suggests that participants used reliable cues for responding to the nominally irrelevant stimulus location if the correct response could be inferred from location (attention switching). By contrast, the lack of cueing effects on performance in noncorresponding conditions of 3-choice tasks suggests that participants cannot use cues for changing the attentional weights of processing channels for different stimulus dimensions (gating). In summary, gating may be involved in the regulation of experienced response conflict, but the present results suggest that it is not involved in the regulation of expected (i.e., predicted) response conflict.     

The influence of dimensional overlap on location-related priming in the Simon task

Choice reaction times are shorter when stimulus and response locations are compatible than when they are incompatible as in the Simon effect. Recent studies revealed that Simon effects are strongly attenuated when there is temporal overlap with a different high-priority task, accompanied by a decrease of early location-related response priming as reflected in the lateralized readiness potential (LRP). The latter result was obtained in a study excluding overlap of stimulus location with any other dimension in the tasks. Independent evidence suggests that location-related priming might be present in conditions with dimensional overlap. Here we tested this prediction in a dual-task experiment supplemented with recording LRPs. The secondary task was either a standard Simon task where irrelevant stimulus location overlapped with dimensions of the primary task or a Stroop-like Simon task including additional overlap of irrelevant and relevant stimulus attributes. At high temporal overlap, there was no Simon effect nor was there stimulus-related response priming in either condition. Therefore stimulus-triggered response priming seems to be abolished in conditions of limited capacity even if the likelihood of an S–R compatibility effect is maximized.     

Enhancement of perceptual representations by endogenous attention biases competition in response selection

Perception and response selection are core processes in the generation of overt behavior. Selective attention is known to facilitate behavioral performance by altering perceptual processes. It remains unclear, however, whether selective attention can aid the resolution of response conflict, and if so, at what stage of processing this takes place. In two experiments, an endogenous cuing task was combined with a flanker task to assess the interaction of selective attention with response selection. The results of Experiment 1 show that cuing reduces the flanker-congruency effect when the cue and flanker are presented in close temporal proximity to each other. The results of Experiment 2 demonstrate that pre- but not post-cuing the target reduced the congruency effect, showing that selective attention can affect performance, but is ineffective once stimulus processing has proceeded to response selection. Our results provide evidence that selective attention can aid the resolution of response conflict by altering early perceptual processing stages.     

The effect of interference in the early processing stages on response inhibition in the stop signal task

In the present study, the relation between interference at the early processing stages and response inhibition was investigated. In previous studies, response stopping appeared to be slowed down when irrelevant distracting information was presented. The purpose of the present study was to further explore the relationship between interference control and response inhibition. In Experiment 1, a stop signal paradigm was combined with a global/local task. The typical global-to-local interference effect is generally attributed to early processing stages, such as stimulus perception and identification. Results of this experiment demonstrated a congruency effect for both reaction time data and zstopping performance. In Experiment 2, these results were replicated with a flanker task that used stimulus-incongruent but response-congruent flankers. Results of both experiments suggest that response inhibition and interference at the early processing stages interact.     

The effect of interference in the early processing stages on response inhibition in the stop signal task

In the present study, the relation between interference at the early processing stages and response inhibition was investigated. In previous studies, response stopping appeared to be slowed down when irrelevant distracting information was presented. The purpose of the present study was to further explore the relationship between interference control and response inhibition. In Experiment 1, a stop signal paradigm was combined with a global/local task. The typical global-to-local interference effect is generally attributed to early processing stages, such as stimulus perception and identification. Results of this experiment demonstrated a congruency effect for both reaction time data and zstopping performance. In Experiment 2, these results were replicated with a flanker task that used stimulus-incongruent but response-congruent flankers. Results of both experiments suggest that response inhibition and interference at the early processing stages interact.     

Co-occurrence of sequential and practice effects in the Simon task: Evidence for two independent mechanisms affecting response selection

The Simon effect refers to the observation that responses to a relevant stimulus dimension are faster and more accurate when the stimulus and response spatially correspond than when they do not, even though stimulus position is irrelevant. Recent findings have suggested that the Simon effect can be strongly modulated by prior practice with a spatially incompatible mapping and by correspondence sequence. Although practice is thought to influence conditional stimulus —response (S-R) processing, leaving response priming through the unconditional route unaffected, sequential effects are thought to represent trial-by-trial adaptations that selectively involve unconditional S —R processing. In the present study, we tested this assumption by assessing the effects of correspondence sequence both when the Simon task alone was performed and when it was preceded by a spatial compatibility task with either incompatible (Experiments 1-2) or compatible (Experiment 2) instructions. The observation that practice and correspondence sequence co-occur and exert additive effects strongly demonstrates that the two factors affect different processing routes.     

Expectancy and stimulus frequency: a comparative analysis in rats and humans.

We examined whether expectancy, one of several factors influencing attention, is similarly affected in rats and humans by manipulation of relative stimulus frequency. A two-choice reaction time (RT) task was developed for rats, and an analogous task was used for humans. Errors, RTs, discriminability, and response bias were measured. Both rats and humans shifted their response bias to the more frequent stimulus, with no change in overall discriminability. As stimulus probability or stimulus repetition increased, RTs and errors decreased. These results illustrate the similarity of expectancy in rats and humans. This two-choice RT task for rats can be used in future studies to examine the neuronal mechanisms of expectancy and attention.     

Attention alters the appearance of motion coherence

Selective attention enhances visual information processing, as measured by behavioral performance and neural activity. However, little is known about its effects on subjective experience. Here, we investigated the effect of transient (exogenous) attention on the appearance of visual motion, using a psychophysical procedure that directly measures appearance and controls for response bias. Observers viewed pairs of moving dot patterns and reported the motion direction of the more coherent pattern. Directing attention (via a peripheral precue) to a stimulus location increased its perceived coherence level and improved performance on a direction discrimination task. In a control experiment, we ruled out response bias by lengthening the time interval between the cue and the stimuli, so that the effect of transient attention could no longer be exerted. Our results are consistent with those of neurophysiological studies showing that attention modulates motion processing and provide evidence of a subjective perceptual correlate of attention, with a concomitant effect on performance.