Speed and accuracy of compensatory responses to limb disturbances

This study examines the speed and accuracy of compensatory responses to flexion-extension perturbations of the wrist in the horizontal plane. In Experiments 1 and 2 the subjects were required to establish an initial flexion or extension force of approximately 15% maximum at a prescribed initial muscle length. The perturbations changed the load force by +/-5% in both simple and choice reaction protocols. The results showed that the latencies to compensate for the perturbation were longer when the direction of disturbance was unknown (i.e., choice effect) and when the perturbation unloaded the muscle (i.e., directional effect). Accuracy constraints on the compensatory response increased movement time and reduced the variability of latency without affecting mean latency. In Experiment 3, a visual stimulus generated a comparable choice effect on latency to that produced by the perturbations, but no directional effect in relation to the preload was apparent. Our behavioral analysis of compensatory responses triggered by wrist perturbations confirms that these responses are susceptible to variables that influence the initiation of voluntary movements. Our analysis also demonstrates a directional preload effect that is stimulus specific.     

Amending movements: the relationship between degree of mechanical disturbance and outcome accuracy

This paper examines the relationship between the degree of a mechanical disturbance, outcome accuracy, and amendment times to produce response corrections. Movement time error and amendment times were generated by systematically increasing the duration of acceleration and deceleration perturbations. Subjects produced discrete timing responses (700 msec-70 degrees) during which perturbations were interjected into the ongoing movement on random trials. Amendment times were generated from acceleration curves along with a number of related kinematic parameters (e.g., Movement Time, Peak Acceleration). The results showed that as the degree of the mechanical disturbance increased, timing error and amendment times to the perturbations also increased. At low force levels, the percentage of accurate responses to a decelerating perturbation was approximately equal to the percentage of accurate responses for control trials. As force level increased, however, timing error increased and the percentage of accurate responses decreased. in addition, as the magnitude of the disturbance increased, changes occurred in the kinematic properties of the perturbed movements which contributed toward the degree of outcome accuracy of the response. Collectively, the results are discussed in relation to an error correction system that operates in an interactive fashion based on the characteristics of the error and the constraints of the task.     

Temporal discrimination and a free-operant psychophysical procedure.

Pigeons were presented a series of keylight time periods (separated by blackouts) during which two response keys were lit, one by blue light and the other either by orange or green. Blue-key responses changed the color on the other key. Orange-key responses sometimes produced food during the first half of a time period; green-key responses sometimes produced food during the second half. In three experiments, the probability of a green-key response increased as a function of elapsed time. Experiment 1 compared performance when the duration of the keylight periods was varied across a wide range. Discrimination of performance was similar across the range of durations. Experiment 2 varied both relative reinforcement rate and the local reinforcement rate for orange-key and green-key responses. These manipulations produced changes in response bias but not discrimination sensitivity. Experiment 3 varied the local temporal placement of reinforcers within time periods and demonstrated that choice behavior was affected by differential reinforcement at different points during the time periods. The results were consistent with previous research on duration discrimination that used psychophysical trials procedures.     

Evidence for Age-related Changes to Temporal Attention and Memory from the Choice Time Production Task

ABSTRACT

The effect of aging on interval timing was examined using a choice time production task, which required participants to choose a key response based on the location of the stimulus, but to delay responding until after a learned time interval. Experiment 1 varied attentional demands of the response choice portion of the task by varying difficulty of stimulus–response mapping. Choice difficulty affected temporal accuracy equally in both age groups, but older participants' response latencies were more variable under more difficult response choice conditions. Experiment 2 tested the contribution of long-term memory to differences in choice time production between age groups over 3 days of testing. Direction of errors in time production between the two age groups diverged over the 3 sessions, but variability did not differ. Results from each experiment separately show age-related changes to attention and memory in temporal processing using different measures and manipulations in the same task.     

Postreinforcement signal processing

Postreinforcement signal processing by rats was demonstrated in six experiments that used a discrete-trials choice procedure. Experiment 1 assessed the extent to which rats are able to transfer knowledge about associations between postreinforcement signal durations and choice responses to conditions where a particular signal duration preceded the opportunity to make a choice response. In Experiment 2 the generality of the transfer effect was demonstrated by using both signal duration and signal modality as relevant stimulus attributes for the postreinforcement signals. The role of the relative durations of the reinforcement-signal gap and the intertrial interval was investigated in Experiment 3. In order to assess the effects of within-trial and between-trial signal relations on the acquisition of a temporal discrimination, both pre-and postreinforcement signals were presented on each trial in Experiments 4 and 5. The effects of pre- and postreinforcement signal relations on the steady-state performance of a temporal bisection task across three different signal ranges were studied in Experiment 6. The conclusion is that rats readily process various stimulus attributes of postreinforcement signals and that relations between postreinforcement signals, choice responses, and prereinforcement signals are major determinants of choice behavior.     

Generalization and response latency

The present experiments investigated generalization in a reaction time situation where the generalization stimulus, a tone, preceded the reaction time signal, a light. The hypotheses under investigation were that the duration of the cue stimulus would determine the degree of generalization (Experiment I) and that the response latency independent of the stimulus duration would be related to the amount of generalization (Experiment II). A particular generalization test stimulus (a tone of 40, 45, 50, 60, 65, or 70 dB) was presented only once always following two bar-pressing responses to training stimulus (tone of 55 dB) under each of two conditions of stimulus duration in Experiment I and under each of two conditions of response latency in Experiment II. It was found that under the condition of short response latency generalization was broader.     

Reaction time and response dynamics

The experiments reported were designed to examine the relationship between reaction time and the response dynamics of a finger-press task. Experiments 1 and 2 manipulated force duration and peak force level in both simple and choice reaction-time paradigms. Experiment 3 constrained both force duration and peak force, leading to independent changes in the rate of force production. The findings from all three experiments suggest that the rate of force production, rather than force duration, is the key response parameter determining reaction time. Reaction time decreased as an exponential function of rate of force production independent of force duration and peak force.     

Backward crosstalk effects in psychological refractory period paradigms: effects of second-task response types on first-task response latencies

Three experiments using psychological refractory period (PRP) tasks documented backward crosstalk effects in which the nature of the second-task response influenced the first-task response latencies. Such effects are difficult to explain within currently popular bottleneck models, according to which second-task response selection does not begin until first-task response selection has finished. In Experiments 1 and 2, the first of the PRP tasks required a choice reaction time (RT) response, whereas the second task required a go/no-go decision. Task 1 responses were faster when the second task required a go response than when it required a no-go response. Experiment 3 showed that Task 1 RTs were also influenced by the complexity of second-task responses. These backward crosstalk effects indicate that significant second-task processing is carried out in time to influence first-task responses and thus challenge strictly serial bottleneck models.     

Generalization and response latency

The present experiments investigated generalization in a reactio? time situation where the generalization stimulus, a tone, preceded the reaction time signal, a light. The hypotheses under investigation were that the duration of the cue stimulus would determine the degree of generalization (Experiment I) and that the response latency independent of the stimulus duration would be related to the amount of generalization (Experiment II). A particular generalization test stimulus (a tone of 40, 45, 50, 60, 65, or 70 dB) was presented only once always following two bar-pressing responses to training stimulus (tone of 55 dB) under each of two conditions of stimulus duration in Experiment I and under each of two conditions of response latency in Experiment II. It was found that under the condition of short response latency generalization was broader.     

Age Preservation of the Syntactic Processor in Production

Two experiments are reported on the influence of cognitive aging on grammatical choice in language production. In both experiments, participants from two age-groups (young and old) produced sentences in a formulation task (V. Ferreira, 1996) that contrasted conditions allowing a choice between alternative sentence arrangements (i.e., double object or prepositional dative) or that permitted no choice (i.e., prepositional dative only). Experiment 1 showed that older adults were able to formulate the alternative sentence arrangements with the same speed and fluency as young adults. Experiment 2 showed that cueing attention to one of the two object nouns to be included in the sentence resulted in the earlier expression of the cued noun in choice conditions, but with little evidence of a response time or dysfluency cost in the no-choice condition. As in Experiment 1, there were no substantive age differences in latencies or dysfluencies. These results support existing models for the mechanisms that choose between grammatical alternatives and bind phrases to available argument positions and provide evidence that older adults are not impaired in their use of these mechanisms.     

Does solution of mental arithmetic problems such as 2 + 6 and 3 x 8 rely on the process of "Memory updating"?

Two experiments are reported that used the selective interference paradigm to study whether, besides response selection, the process of memory updating is involved in simple mental arithmetic. Participants were asked to solve simple sums (e.g., 2 + 6, Experiment 1) or simple products (e.g., 3 X 8, Experiment 2) in a single-task control condition and in three dual-task conditions with a selective interference task, simple reactions, choice reactions, or delayed choice reactions. The role of memory updating was estimated on the basis of the difference in impairment due to the choice reaction time and the delayed choice reaction time task, whereas the difference in impairment between the simple reaction time and the choice reaction time task indicates the role of response selection. While replicating previous results concerning response selection (Deschuyteneer & Vandierendonck, 2005, in press), the study showed that memory updating is strongly involved in solving simple mental arithmetic sums and products.     

The gap effect for eye and hand movements

A temporal gap between fixation point offset and stimulus onset typically yields shorter saccadic latencies to the stimulus than if the fixation stimulus remained on. Several researchers have explored the extent to which this gap also reduces latencies of other responses but have failed to find a gap effect isolated from general warning effects. Experiment 1, however, showed a robust gap effect for aimed hand movements (which required determination of a precise spatial location), regardless of whether the hand moved alone or was accompanied by a saccadic eye movement. Experiment 2 replicated this aimed hand gap effect and also showed a smaller effect for choice manual keypress responses (which required determination of the direction of response only). Experiment 3 showed no gap effect for simple manual keypress responses (which required no spatial determination). The results are consistent with an interpretation of the gap effect in terms of facilitation of spatially oriented responses.     

Timeout from concurrent schedules.

Response-contingent timeouts of equal duration and frequency were added to both alternatives of unequal concurrent schedules of reinforcement. For each of 4 pigeons in Experiment 1, relative response rates generally became less extreme as the frequency of timeout increased. In Experiment 2, relative response rates consistently approached indifference as the duration of timeout was increased. Variation in time allocation was less consistent in both experiments. Absolute response rates did not vary with the timeout contingency in either experiment. In a third experiment, neither measure of choice varied systematically when the duration of a postreinforcement blackout was varied. In contrast to the present results, preference has been shown to vary directly with the parameters of shock delivery in related procedures. The pattern of results in the first two experiments follows that obtained with other manipulations of the overall rate of reinforcement in concurrent schedules. The results of the third experiment suggest that an intertrial interval following reinforcement is not a critical feature of the overall rate of reinforcement.     

Aging and working memory inside and outside the focus of attention: dissociations of availability and accessibility

Two experiments used the N-Back task to test for age differences in working memory inside and outside the focus of attention. Manipulations of the difficulty of item-context binding (Experiment 1) and of stimulus feature binding (Experiment 2) were used to create conditions that varied in their demand on working memory, with the expectation that greater demand might increase age differences in focus-switching costs and the search rate outside the focus of attention. Results showed, however, that although age differences were evident in measures of overall speed and accuracy, and the manipulations significantly affected response times and accuracy in the expected direction, the experimental manipulations had no impact on age differences. Findings instead pointed to age-related reductions in accuracy but not speed of focus-switching and search outside the focus of attention. Thus, age-related deficits appear to involve the availability of representations in working memory, but not their accessibility.     

Distributed Control in Rapid Sequential Aiming Responses

The preparation and on-line control of short, rapid sequential aiming responses were studied in 3 experiments. Participants (N = 12 in Experiments 1 and 2, and 20 in Experiment 3) produced 3-segment responses (a) within self-initiation, simple reaction time (RT), and choice RT paradigms (Experiment 1); (b) without visual feedback under self-initiation conditions (Experiment 2); and (c) with and without visual feedback under simple RT conditions (Experiment 3). In all conditions in which participants initiated movement in response to an external imperative signal, the 2nd response segment was performed consistently slower than preceding and succeeding response segments. That pattern of segmental movement times was found whether or not visual feedback was available but was not evident when participants self-initiated their responses with or without visual feedback. The findings rule out the possibility that subjects' use of visual feedback is responsible for the slowing of the 2nd response segment under RT conditions and suggest that the programming of rapid sequential aiming responses can be distributed in pre- and postinitiation intervals.     

Separating the effects of interreinforcement time and number of interreinforcement responses

The relative importance of interreinforcement time and interreinforcement responses was evaluated by varying each independently. To do this, a blackout was presented after each nonreinforced response under both fixed-ratio and fixed-interval schedules of reinforcement. Manipulating the blackout duration under the fixed-ratio schedule caused interreinforcement time to vary without affecting the number of interreinforcement responses. Pigeons' post-reinforcement and post-blackout response latencies were found to increase linearly with interreinforcement time. Under the fixed-interval schedule, the same blackout manipulations changed the number of interreinforcement responses without affecting interreinforcement time. Post-reinforcement and post-blackout response latencies under this condition were approximately constant. These results suggest that responding is controlled by interreinforcement time and is not influenced by the number of responses emitted between reinforcements.     

Attentional strategic control over nonlexical and lexical processing in written spelling to dictation in adults

We conducted four experiments to investigate whether adults can exert attentional strategic control over nonlexical and lexical processing in written spelling to dictation. In Experiment 1, regular and irregular words were produced either in a nonword context (regular and irregular nonwords) or in a word context (high-frequency regular and irregular words), whereas in Experiment 2, the same set of words was produced either in a regular nonword or in an irregular low-frequency word context. Experiment 3 was a replication of Experiment 2 but with increased manipulation of the context. In Experiment 4, participants had to produce either under time pressure or in response to standard written spelling instructions. Regularity effects were found in all the experiments, but their size was not reliably affected by manipulations intended to increase or decrease reliance on nonlexical processing. More particularly, the results from Experiment 4 show that adults can speed up the initialization of their writing responses to a substantial degree without altering regularity effects on either latencies or spelling errors. Our findings suggest that, although adults are able to generate an internal deadline criterion of when to initialize the writing responses, nonlexical processing is a mandatory process that is not subject to attentional strategic control in written spelling to dictation.     

Effect of uncertainty on the time course for selection of verbal name codes

Response selection takes time. Hick's law (Hick, 1952) predicts that the time course of response selection is a logarithmic function of the number of equally likely response alternatives. However, recent work has shown that oculomotor responses constitute noteworthy exceptions in that the latencies of saccades (Kveraga, Boucher, & Hughes, 2002) and smooth pursuit movements (Berryhill, Kveraga, Boucher, & Hughes, 2004) are completely independent of response uncertainty. This finding extends to the case in which the required response was known in advance (i.e., simple reaction times [RTs] were equivalent to choice RTs). In view of these results, we reevaluated reports that latencies to name visually presented digits (Experiment 1) and/or repeat aurally presented digits (Experiment 2) are similarly independent of the size of the response set. We found that naming latencies were equivalent for response set sizes from one to eight, but simple RTs (response set of one) were faster. Thus, the overlearned task of digit naming is indeed highly automatic but has not reached the level of automaticity characteristic of the oculomotor system.     

Sensitivity to reinforcer duration in a self-control procedure

In a concurrent-chains procedure, pigeons' responses on left and right keys were followed by reinforcers of different durations at different delays following the choice responses. Three pairs of reinforcer delays were arranged in each session, and reinforcer durations were varied over conditions. In Experiment 1 reinforcer delays were unequal, and in Experiment 2 reinforcer delays were equal. In Experiment 1 preference reversal was demonstrated in that an immediate short reinforcer was chosen more frequently than a longer reinforcer delayed 6 s from the choice, whereas the longer reinforcer was chosen more frequently when delays to both reinforcers were lengthened. In both experiments, choice responding was more sensitive to variations in reinforcer duration at overall longer reinforcer delays than at overall shorter reinforcer delays, independently of whether fixed-interval or variable-interval schedules were arranged in the choice phase. We concluded that preference reversal results from a change in sensitivity of choice responding to ratios of reinforcer duration as the delays to both reinforcers are lengthened.     

Dissociation between Categorical and Coordinate Spatial Computations: Modulation by Cerebral Hemispheres, Task Properties, Mode of Response, and Age

Kosslyn suggested a dissociation of two kinds of spatial representations: categorical and coordinate, the former computed by the left hemisphere and the latter by the right hemisphere. In addition, with practice, a “categorization” of the coordinate computation would appear. These suggestions resulted largely from an experiment, replicated by others, in which the subjects had to estimate the relative position of a dot and a line by giving an oral response, and feedback was provided. The present series of five experiments was an attempt to test whether this finding could be generalized, under several methodological manipulations, some of which have already been used by researchers in separate studies. In the five experiments, accuracy was a more contributive dependent variable than correct latencies, and practice effects on the task × field interaction were not verified. Experiments 1–3 concerned the kind of response. When a manual instead of an oral response was required (Experiment 1;n= 32 Ss), the expected dissociation was observed (as well as when the latency of responses made by the right hand were studied). When the number of oral responses was increased from two (a binary choice) to eight, the dissociation was still observed for accuracy but disappeared when a more liberal criterion of accuracy was used to reduce the considerable task effect (Experiment 2;n= 32 Ss), or when response requirements were equated for both tasks (Experiment 3;n= 32 Ss). In Experiment 4 (n= 32 Ss), a manual response was called but the feedback was removed and the task dissociation disappeared. Finally, the task dissociation observed in Experiment 1 was not verified when a sample of elderly subjects was enrolled (Experiment 5;n= 32 Ss). However, age per se was the source of an interesting additional dissociation since only the coordinate computation was age sensitive. Our results suggest that the dissociation proposed by Kosslyn between the computation of categorical vs coordinate spatial relationships is highly unstable and sensitive to subtle methodological factors (vocal vs manual response, presence vs absence of feedback, binary vs “continous” response, age) which could preclude its general application.