The effect of response force on avoidance rate

In a Sidman-avoidance schedule of counter losses for two human subjects, the loss-to-loss and response-to-loss intervals were 20 sec. The avoidance response was a vocal response that was louder than a minimum vocal requirement. This requirement was set at 80 db, 95 db, or 110 db. In addition to vocal responses meeting the minimum requirement, all responses exceeding a threshold of 75 db or louder were recorded. The rate of both above-threshold and avoidance responses decreased as the response-force requirement increased. Thus, high response-force requirements produced an effect on avoidance responding similar to its effect on positively reinforced responding.     

The SYBAR system: Integrated recording and display of video, EMG, and force plate data

A new system—called SYBAR—is introduced, that employs digital video for registration of the movements of a patient while simultaneously recording electromyogram signals of relevant muscles and ground reaction forces (for the lower extremities in gait studies). All information is stored in a multimedia record, which can be viewed by the clinician with a simple user interface. This setup allows an integrated and more detailed view of the movement of the patient and related information (i.e., muscle physiology). It is used by clinicians to assess the causes of movement disorders in their patients. This paper describes the SYBAR system and focuses on the employed methods of data synchronization for both the time and the spatial domains. It is concluded that, although SYBAR was developed for clinical gait studies, the technology can be applied in all situations in which the relation between physiological signals and human or animal behavior is studied.     

The duration of response inhibition in the stop-signal paradigm varies with response force

In a previous study, we have found that the speed of stopping a response is delayed when response readiness is reduced by cuing the probability of no-go trials [Acta Psychol. 111 (2002) 155]. Other investigators observed that responses are more forceful when the probability to respond is low than when it is high (e.g. [Quart. J. Exp. Psychol. A 50 (1997) 405]). In this study, the hypothesis was tested that low probability responses are more forceful than high probability responses and that these responses are more difficult to stop. Subjects performed on a choice reaction task and on three tasks with respectively 100%, 80%, and 50% response probabilities. Stop signals were presented on 30% of the trials, instructing subjects to withhold their response. Response force on non-signal (go) trials and the duration of response inhibition on signal (stop) trials increased as response probability decreased. This pattern of findings was interpreted to support the hypothesis predicting that stopping is more difficult when response readiness is low than when it is high.     

Quantification of manual force control and tremor

Isometric impulse frequencies associated with active tremor and force regulation were examined in 10 patients with idiopathic Parkinson's disease (PD) and in 10 older adults (OAs) who performed an isometric tracing task. The authors decoupled and analyzed the data to determine whether PD-related tremor in the thumb and in the index finger during isometric force control are related and whether PD impairs the performance of volitional force control beyond the errors contributed by tremor. After decoupling, there were clear and robust differences in PD patients' control of isometric force that could not be attributed to action-tremor error. Those errors, which occurred in the absence of movement, suggest impairment in coordinated recruitment and derecruitment of motor units during a fine-motor task.     

Use of a notation system for digital control and recording

This paper describes (1) a notation system for digital control and recording, (2) some improvements to SKED, and (3) future developments and uses of minicomputers.     

The role of response force on the persistence and structure of behavior during extinction

Behavior Momentum Theory has emerged as a prominent account of resistance to change in both basic and applied research. Although laboratory studies often define precise, repeatable responses, application research often deals with response classes that may vary widely along a number of dimensions. In general, Behavior Momentum Theory has not addressed how response dimensions impact resistance to change, providing an opportunity to expand the model in new directions. Four rats pressed a force transducer under a multiple variable interval (VI) 60‐s VI 60‐s schedule of reinforcement. In one component, responses satisfied the schedule only if the response force fell within a “low” force band requirement; responses in the other schedule were required to satisfy a “high” force band. Once responding stabilized, extinction was programmed for three sessions. Then, the procedures were replicated. The results showed that response force came under discriminative control, but force requirements had no impact on resistance to extinction. In a follow‐up condition, the schedule was changed to a multiple VI 30‐s VI 120‐s schedule and the low‐force band operated in both components. The results showed that behavior maintained by the VI 30‐s schedule was generally more resistant to extinction. A secondary analysis showed that force distributions created under baseline maintained during extinction. Overall, the results suggest that differential response force requirements prevailing in steady state do not affect the course of extinction.     

A microprocessor control and recording system for instrumental behavior research

This paper describes a miroprocessor system developed for experimental control and data collection in real time. By connecting the experimental equipment to the microprocessor via a serial communication interface, transmission of various animal test-chamber functions over greater distances with only a few cables is facilitated. The microprocessor is programmed on a host computer (PDP/8). A combined terminal station with a cassette deck is used for data and program storage.     

The measurement of response force during a lever-press shock-escape procedure in rats

Three albino rats were given extensive exposure to an escape procedure in which shocks were scheduled to occur 30 sec apart. The amount of downward force exerted on the lever was continuously recorded and compared with traditional discrete measurement in which only responses above an arbitrary force threshold were recorded. Subjects typically remained in contact with the lever throughout the shock-free intertrial interval. Shock onset reliably occasioned a brief lurch from and return to the lever, which resulted in a lever-press escape response being recorded. Lever contact, which occupied an average of 90% of session time, showed great stability in force after a brief (e.g., 5-sec) period of instability after each shock terminated. In general, continuous measurement revealed considerably different results than discrete measurements of on-lever behavior. For example, continuous lever contact fluctuating near response threshold was often recorded as discrete responding, and sustained lever contact occurring below response threshold was omitted from discrete measurement.     

Asymmetric control of force and symmetric control of timing in bimanual finger tapping

An experiment was conducted to examine the control of force and timing in bimanual finger tapping. Participants were trained to produce both unimanual (left or right hand) and bimanual finger-tapping sequences with a peak force of 200 g and an intertap interval (ITI) of 400 ms. During practice, visual force feedback was provided pertaining to the hand performing the unimanual tapping sequences and to either the dominant or the nondominant hand in the bimanual tapping sequences. After practice, the participants produced the learned unimanual and bimanual tapping sequences in the absence of feedback. In those trials the force produced by the dominant (right) hand was significantly larger than that produced by the nondominant (left) hand, in the absence of a significant difference between the ITIs produced by both hands. Furthermore, after unilateral feedback had been provided of the force produced by the nondominant hand, the force output of the dominant hand was significantly more variable than that of the nondominant hand. In contrast, after feedback had been provided of the force produced by the dominant hand, the variability of the force outputs of the two hands did not differ significantly. These results were discussed in the light of both neurophysiological and anatomical findings, and were interpreted to imply that the control of timing (in bimanual tasks) may be more tightly coupled in the motor system than the control of force.     

Grasp force control in older adults

Diminished tactile sensibility and impaired hand dexterity have been reported for elderly individuals. Reports that younger adults with severely impaired tactile sensibility use excessive grasp force during routine grasp and manipulation tasks raise the possibility that elderly persons likewise produce large grasp forces that may contribute to impaired dexterity. Impaired pseudomotor functioning also occurs in elderly subjects and may yield a slipperier skin surface that enhances the possibility for excessive grasp force. The present study measured grasp force in 10 elderly and 9 young adult individuals, during grasp and vertical lift of a small object, using a precision (pinch) grip of the thumb and index finger. The slipperiness of the object's gripped surfaces was unexpectedly varied. Skin slipperiness was estimated by also measuring the grasp force at which the object slipped from grasp. The older subjects employed grasp forces that were, on average, twice as large as those of the young subjects, with some producing forces many times greater than the young subjects' average grip force. Grip forces also were significantly more variable across trials in older subjects. This increased variability was not caused simply by the elderly subjects' increased grip force. A portion of the increased force was due to increased skin slipperiness. The grip force that the elderly subjects produced in excess of the slip force (the "margin of safety" against object slippage) was larger than would have been predicted from their skin slipperiness, however. It is suggested that, in part, the excessive grasp forces represent a strategic response to tactile sensibility impairment. Twopoint discrimination limina in the older subjects averaged about four times greater than in the younger subjects. Increased grasp forces in elderly persons may result from other factors, such as increased variability in grip force production. The contributions of excessive grasp forces to impaired dexterity in older persons still need to be addressed experimentally.     

Early-extinction effects on a force response of humans

Humans were used to investigate changes in response force occurring soon after reinforcement was eliminated. In Experiment 1, in a 300-s baseline phase, 10 participants received a point for holding down a pressure sensor set to operate at a force equal to 85% of the maximum force the participants exerted during a pretest. Following this, during a 600-s extinction phase, criterion responses had no consequence. In Experiment 2, 6 participants worked on the same task, but (a) points were exchangeable for money and (b) after extinction, the reinforcement baseline phase was reinstated. In Experiment 3, 6 participants completed the same task as in Experiment 2, but the required minimum force was 60% of the maximum force exerted during the pretest. In each experiment, increases in response force relative to the mean and peak force exerted during the last 100 s of baseline were observed in most participants when force responses were aggregated into short sample intervals, but less so with longer ones. The increases, however, were not systematic across or within participants, questioning the generality of and the criteria for demonstrating an extinction burst.     

Effects of force levels on error compensation in periodic bimanual isometric force control

ABSTRACT The authors examined whether force level interacts with the presence or absence of vision in bimanual force control. Participants produced periodic isometric forces such that the sum of the 2 finger forces was the target force under 4 force levels cycling between lower levels (5-40%) of maximum voluntary contraction with an interval of 1000?ms. Without vision, the correlation between the 2 finger forces was strongly positive over all force levels. However, with vision the correlation changed from negative to positive with force level. The result with vision indicated that the strategy of the bimanual force control changed from force error compensation to force coupling and the available redundancy thus decreased with an increase in force.     

Comparing stimulus preference and response force in a conjugate preparation

Researchers used a conjugate preparation to evaluate how response force changed based on participants' preferences for visual stimuli. First, researchers used a verbal preference assessment to evaluate each participant's preference for viewing for five object categories of visual stimuli; this process identified high preference (HP) stimuli and low preference stimuli for most participants. Thereafter, researchers exposed each participant to the five stimulus categories in a randomized order while using a force dynamometer to measure their response force to increase visual clarity of each stimulus. Results indicate the majority of participants' HP stimuli corresponded to the stimulus category for which they exerted the highest mean force. These preliminary findings suggest conjugate preparations involving response force may provide another option for measuring the relative value of some stimulus events.     

Fractioned reaction time as a function of response force

The relationship between fractionated reaction time components and response force was studied in a simple reaction time task. Subjects squeezed a force transducer between the right thumb and index finger. Three conditions with 5, 25, and 50% of the maximum voluntary isometric force were investigated in a counterbalanced order. The results showed that premotor reaction time was negatively related to peak force amplitude, while motor reaction time remained constant across force conditions. An interpretation of the effect on premotor reaction time in terms of a shift in the speed-accuracy trade-off function was refuted. Although the data were consistent with a two-stage programming model, it was concluded that differences in motor nerve fiber conduction velocity as a function of response force could explain the results obtained.     

Emotional reactivity and force control: the influence of behavioral inhibition

Individual difference measures have been shown to alter emotional arousal and emotional arousal alters force production during force control tasks. In the current study we examined whether individual differences in behavioral inhibition influence force control during emotional image viewing. Subjects who scored high and low in behavioral inhibition (BIS) produced force with visual feedback for 5 s. Feedback was then removed and replaced by a mutilation, attack, erotica, or neutral image for 6 s. The magnitude and direction of error in force production during image presentation was compared between groups and across image type. The high BIS group displayed a relative increase in force production during exposure to attack and mutilation images compared to the low BIS group. Bias scores (i.e., comparison of unpleasant image to neutral or pleasant image) further confirmed these findings by demonstrating a relative increase in force for the high BIS group during attack and mutilation images as compared to erotica images, whereas the low BIS group displayed the reverse effect. Together these findings extend the premise of action readiness to demonstrate that dispositional differences in behavioral inhibition interact with emotional state to alter force production.     

Effects of focal basal ganglia lesions on timing and force control

Studies of basal ganglia dysfunction in humans have generally involved patients with degenerative disorders, notably Parkinson's disease. In many instances, the performance of these patients is compared to that of patients with focal lesions of other brain structures such as the cerebellum. In the present report, we studied the performance of patients with focal basal ganglia lesions on three fundamental motor tasks. The patients all had suffered unilateral damage in the striatum and were tested in the chronic state. The first task required the participants to tap with their index finger as fast as possible; this test provided a simple assessment of motor competence. Compared to controls, the maximum tapping rate was lower for the patients when tapping with their contralesional limb, although the deficit was not severe. The second and third tasks were designed to assess timing and force control, two functions that have been associated with basal ganglia function. The patients performed similar to controls on both tasks and showed no evidence of impairment when using their contralesional limb compared to their ipsilesional limb. The results indicate that unilateral basal ganglia lesions tend to produce minor motor problems in force control, and fail to support the hypothesized role of the basal ganglia in timing.     

Perceptual influences of error size on voluntary force control during a compound sinusoidal force task

Visual feedback that provides error information is critical to task quality and motor adjustments. This study investigated how the size of perceived errors via visual feedback affected rate control and force gradation strategy of a designate force task. Fourteen young adults coupled force exertions to a compound sinusoidal signal (0.2 Hz and 0.5 Hz) that fluctuated around a mean level of 30% of maximal voluntary contraction, when the size of execution errors were differently scaled with the error amplification factors. In the low (LAF) and high (HAF) amplification factor conditions, the execution errors in the visual display half and double of the real errors, respectively. The visualized error was the real errors in the medium amplification factor (MAF) condition. In addition to a phase-lead of force output, the LAF condition that virtually reduced the size of error feedback associated with a poorer task accuracy than the MAF and HAF conditions. Virtual increase in error size of visual feedback selectively suppressed the fast target force at 0.5 Hz. In addition, complexity and high-frequency components (>0.75 Hz) of force outputs multiplied progressively with increasing error size. Error-enhancing feedback suppressed fast target force, accentuating the use of error information to tune force output, whereas error-reducing feedback enhanced fast target force in favor of predictive force control.