Allen D. Szalda-Petree

A Comparison of Four Tests of Malingering and the Effects of Coaching

This study examined the ability of four measures of suboptimal performance to correctly classify four groups of subjects (normal controls, uncoached malingering, coached malingering, and head injured). Only the Portland Digit Recognition Test-Computerized (PDRT-C) identified simulating malingerers with greater than chance accuracy while minimizing false positives. Coached subjects were better able than their uncoached counterparts to avoid detection on all measures. In an additional analysis, a discriminant function using the response latency and total correct scores from the PDRT-C identified 70% of the coached malingerers on cross validation. The three other tests (Nonverbal Forced Choice Test, 21-Item Test, and Dot Counting Test) failed to obtain a satisfactory classification rate for the malingering groups as a whole and coached malingerers in particular.

PORTLAND DIGIT RECOGNITION TEST-COMPUTERIZED: MEASURING RESPONSE LATENCY IMPROVES THE DETECTION OF MALINGERING

Abstract This study assessed the use of response latency as an aid in the detection of malingering using a computerized version of the Portland Digit Recognition Test (PDRT-C). Two groups of 30 college student malingerers (one coached and one uncoached), 30 head-injury patients (CHI), and 30 age-and education-matched controls were administered the PDRT-C. A discriminant function using the total correct and response latency data successfully classified 74% of the malingerers and 100% of the CHI and normal control subjects on validation. Coached malingerers were more successful at avoiding detection than uncoached malingerers. However, the detection of coached malingerers rose from 47% to 70% by measuring response latency. Overall, 32% fewer errors were made using the total correct and response latency data when compared to classification rates using the total correct score alone.

Self-control in rhesus macaques (Macaca mulatta): controlling for differential stimulus exposure.

Previous research on self-control using macaques (Macaca fascicularis) showed these animals have a strong bias for a delayed, larger reinforcer (Self-control) over an immediate, smaller reinforcer (Impulsive). Typical studies of self-control have used a discrete trials methodology with a secondary discriminative stimulus during the delay periods. This results in a greater exposure to the stimulus representing the self-controlled option and may account for some of the early exclusive preference for self-control observed. The present experiment examined self-control bias in three rhesus macaques (Macaca mulatta) while controlling for differential durations of stimulus exposure. Subjects were presented stimuli via a computer monitor and made choices by touching the stimulus at which point both stimuli were removed for the delay periods. All three subjects displayed a nearly exclusive bias for the delayed, larger reinforcer (self-control). These results are consistent with previous studies, despite the variations in methodology and species.

Risk-sensitive foraging in rats: the effects of response-effort and reward-amount manipulations on choice behavior.

The literature on risk-sensitive foraging theory provides several accounts of species that fluctuate between risk-averse and risk-prone strategies. The daily energy budget rule suggests that shifts in foraging strategy are precipitated by changes in the foragers energy budget. Researchers have attempted to alter the organisms energy budget using a variety of techniques such as food deprivation, manipulation of ambient temperatures, and delays to food reward; however, response-effort manipulations have been relatively neglected. A choice preparation using a wheel-running response and rats examined risk-sensitive preferences when both response effort and reward amounts were manipulated. Concurrently available reinforcement schedules (FI/60 and VI/60) yielded equivalent food amounts per unit time in all treatments. Two levels of response effort (20 or 120 g tangential resistance) and two levels of reward amount (three or nine pellets) were combined to form four distinct response-effort/reward-amount pairings. Increasing reward amounts significantly shifted choice toward the FI schedule in both response-effort conditions. The incidence of choice preference and the magnitude of shifts in choice were greater for the high response-effort conditions than for the low response-effort conditions. Implications of the significant interaction between response effort and reward amount are discussed in terms of a general energy-budget model.

Sex Differences in Risk Sensitivity Under Positive and Negative Budgets and Predictors of Choice

The authors investigated sex differences in human risk sensitivity by using a computerized choice task with an energy budget analogue. In addition, they explored possible personality predictors of variance sensitivity. The authors modified the traditional energy budget model from those used in risk-sensitive foraging research with nonhuman animals for appropriate use with a human population. Participants chose between 2 computer icons, 1 yielding a fixed-point reward and the other offering variable points. Men were risk prone in the negative budget and risk averse in the positive budget. Women were risk averse in the negative budget. Personality was not predictive of risk-sensitive bias. Interpreting the results using an evolutionary model, the authors found support for a biological and environmental construct of risk-sensitive behavior.

Instrumental conditioning of choice behavior in male Siamese fighting fish (Betta splendens)

Despite the differences in the response of male Betta splendens toward various stimuli, no research has attempted to determine the preference for a live conspecific versus a mirror presentation. A submerged T-maze was used to present both stimuli to healthy male B. splendens (N=16). The results indicated that subjects start box and swimway latencies decreased significantly over the 30 trials. Moreover, the analysis of choices demonstrated a modest, but statistically significant, preference for the live conspecific over the mirror presentation. The results are discussed in terms of the stimuli qualities that elicit an aggressive response in B. splendens and the implications for common experimental procedures.

Wheel-running in discrete trial and operant paradigms under various effort requirements

Two experiments were conducted in which the wheel-running behavior of rats under various effort requirements was investigated. The specific effort requirements were obtained by varying the tangential force required to initiate wheel movement. In the first experiment, a discrete trial preparation was used in which 4 groups of rats received training with high effort levels of 90, 110, 130, and 150 g. The results showed that increasing effort requirements slowed the rate of acquisition, lowered the asymptotic running speeds, and reduced resistance to extinction. In the second experiment, using an operant preparation, running speeds were examined for baseline (nonreinforced) and fixed-interval 1 min schedules of reinforcement at effort levels of 45, 90, and 180 g. The results clearly showed wheel-running to be schedule-induced. However, the effects of effort on FI behavior were less clear due to inconsistencies between subjects. Results are discussed in terms of the potential benefits of bridging operant and discrete trial preparations and methods for studying the effects of effort on animal behavior.

Increased effort requirements and risk sensitivity: a comparison of delay and magnitude manipulations

Reward magnitude and delay to reward were independently manipulated in two separate experiments examining risk-sensitive choice in rats. A dual-running wheel apparatus was used and the tangential force resistance required to displace both wheels was low (50g) for half of the subjects, and high (120g) for the remaining subjects. Concurrent FI30-s and FI60-s schedules delivered equivalent amounts of food reward per unit time (i.e. 5 and 10 pellets of food, respectively), and these conditions served as the baseline treatment for all subjects. Variability, either in reward magnitude or delay, was introduced on the long-delay (60s) schedule during the second phase. All subjects were returned to the baseline condition in the third phase, and variability was introduced on the short-delay (30s) interval schedule during phase four. The subjects were again returned to the baseline condition in the fifth and final phase, ultimately yielding a five-phase ABACA design. Original baseline performance was characterized by a slight short-delay interval preference, and this pattern of performance was recovered with each subsequent presentation of the baseline condition. Overall, the data obtained from the reward magnitude and delay-to-reward manipulations were indistinguishable; subjects experiencing low-response effort requirement behaved in a risk-indifferent manner and subjects experiencing high-response effort requirement preferred the variable schedule. Implications for the daily energy budget rule on risk-sensitive foraging are discussed in light of these findings.

Behavioral effects of fluoxetine on aggression and associative learning in Siamese fighting fish (Betta splendens)

Past research has implicated serotonin as an important neurotransmitter in the facilitation of aggressive behavior. In Siamese fighting fish (Betta splendens), the SSRI fluoxetine has been demonstrated to reduce both frequency and duration of aggressive displays across a variety of concentration exposure procedures. While this multi-method approach has provided strong evidence for fluoxetines impact on aggression, no study has sought to examine the behavioral mechanism by which fluoxetine exerts its anti-aggressive effect. To address this question, a Go-No Go discrimination task utilizing mirror presentations as a reinforcer was designed. Consistent with previous reports, the results indicated that fluoxetine may exert a sedative effect upon aggressive behavior via decreased arousal to external stimuli.

Monitoring running-wheel movement using a serial mouse and an IBM-compatible system

A running-wheel-movement-detection system is described for use with an IBM-compatible system and a serial mouse. It is an adaptation of a system developed for use on a Commodore 64. The IBM-compatible system provides obvious advantages in speed, memory, data storage, and programming ease over the earlier Commodore 64 system.