Naloxone administration impairs autoshaped learning

Effects of naloxone on acquisition of autoshaped behavior were investigated. Rats deprived to 85% of free-feeding weights were trained to touch a retractable lever; delivery of a food pellet occurred on every trial following lever retraction. The lever was retracted immediately if a touch occurred within 15 s, or automatically after 15 s. Analyses were conducted on number and latencies of touches of the extended lever, nose-pokes (touches) directed at the retracted lever during intertrial intervals (a measure less constrained by ceiling effects than extended lever touches), and unconditioned exploratory rearing activity, measured as touches of a metal strip mounted above the grid floor of the apparatus. In an initial experiment, male Sprague-Dawley rats were given saline or naloxone (2.0 mg/kg, ip) 5 min before a training session of 12 trials. Two days later they were tested, in the absence of drug, in a session of 36 (three blocks of 12) trials. Naloxone depressed training levels of lever responding, in addition to slowing acquisition rate. No effect of naloxone was observed on rearing activity. Previous work showed that injection of saline 5 min before behavioral testing increases the rate of autoshaping compared to injections 30 min before (Messing & Sparber, 1984). Thus, effects of naloxone on acquisition of lever-directed behaviors may have been confounded by behavioral depressant effects and/or by an injection effect such a short time before testing. In a second experiment naloxone (0.5 or 2.0 mg/kg) was injected after five of seven training sessions (12 trials each) to male and female rats. A 6-s delay of reinforcement was inserted between lever retraction and food delivery, slowing acquisition rates and providing the opportunity to test the effects of naloxone throughout a multiple-session task. The low dose retarded acquisition of extended lever touching in both sexes; both doses retarded acquisition of interim lever touching in males. Thus, in some circumstances, post-training naloxone administration may impair learning. The results support the notion that low doses of naloxone may have agonist activity.     

The effects of alcohol and delta-9-tetrahydrocannabinol on human physical aggression

Forty male undergraduates were provoked following their ingestion of high or low doses of either alcohol or delta-9-tetrahydrocannabinol (THC). The expression of physical aggression was related to the quantity of alcohol ingested. The high dose of alcohol instigated more intense aggression than the low dose. The high dose of THC, on the other hand, did not increase aggressive behavior. In fact, it tended to produce a weak suppression effect.     

Differences between students' estimated and attained grades in a first-year introductory psychology course as a function of identity development

Two hundred sixty-eight first-year university students were surveyed about the state of their identity development and their perceptions regarding chances for academic success in an introductory psychology course. In general, it was found that students who had an adult identity had a more accurate assessment of their chances for success in the course and also used more efficient study strategies. Students who had not completely formed an adult identity, however, were more inaccurate in estimates of their final grades and also seemed to use less productive study strategies. It was concluded that those who have formulated an adult identity might have also developed a more complete understanding of both themselves and their situation. Implications of the findings for further research regarding the effects of identity development on university life, as well as the implications for academic intervention programs, are discussed.     

Selective exposure and dissonance after decisions

Well-known literature reviews from the 1960s question whether cognitive dissonance underlies experimental participants' selective exposure of themselves to consonant messages and avoidance of dissonant ones. A meta-analytic review of 16 studies published from 1956 to 1996 and involving 1,922 total participants shows that experimental tests consistently support the supposition that dissonance is associated with selective exposure (r = .22, p < .001). Statistical power exceeded .99. Advances in statistical methodology and increased attention to selecting appropriate tests of dissonance theory were essential to finally resolving this question.     

Perception and production of rise-fall intonation in American English

At the segmental level, the rate of speaking affects the degree of physical undershoot of articulatory targets and the resulting perception. Little is known regarding evidence of these effects at the suprasegmental level, particularly in intonation. In this study, the effect of rate of speaking on fundamental frequency and on perceptual judgments of peak pitch in a rise-fall intonation pattern was investigated. First, speakers produced rise-fall intonations in sentence contexts at slow, normal, and fast speaking rates. Peak fundamental frequencies (F0) of the slow productions were significantly lower than those of the normal or fast productions. The mean normal rate production of the word Miami was used as a model for the target word in a series of subsequent perceptual experiments. Altering the duration of the target word to represent slow, normal, and fast rates of speaking did not affect listener judgment of peak pitch. Finally, the pitch of the target word was measured in a sentence context. No differences between peak pitch in isolation or in sentence context were found. It was concluded that the production and perception of this form of intonation was not subject to the effects of rate that are seen at the segmental level.     

Specificity of the MMPI-2 Fake Bad Scale as a marker for personal injury malingering

Psychologists who evaluate patients in medicolegal contexts should utilize objective assessment data with empirically established sensitivity and specificity for identifying negative response bias. The purpose of this study was to investigate the specificity of the Fake Bad Scale for identifying negative response bias in personal injury claimants. The cutoff scores proposed by Lees-Haley and colleagues were applied a federal prison, medical outpatients, and patients from to inmate volunteers from substance abuse unit. Half of the inmates were given instructions to malinger psychopathology to affect the adjudication process, and the remaining inmates and all of the hospital patients were given standard instructions. The original cutoff scores correctly identified the majority of inmates instructed to malinger psychopathology, but these scores resulted in unacceptably high rates of false positive classifications. The revised cutoff scores resulted in fewer false positives, i.e., 8%-24%.     

Stem homographs and lemma level representations

Previous studies have found that priming a target like cerr-o ("hill") with an unmasked stem-homograph (e.g., cerr-ar, "to close") or with an unmasked allomorph of a stem-homograph (e.g., cierr-a, "he/she/it closes") has an inhibitory effect on target recognition. We report evidence from stem-homograph priming studies that implicate both morphological parsing and lexical selection processes at the lemma level. We argue that stem-homograph inhibition is the product of lexical selection mechanisms that are engaged just when a fully ambiguous stimulus (here, an inflectional stem) must be assigned one of its viable interpretations in order to afford conscious perception of lexical identity.     

Action-based and vision-based selection of input: Two sources of control

In the first part of this paper we review evidence suggesting that there exists a mechanism that selects input on the basis of its similarity to the required action. This response-based input selection differs from the more established space- and object-based input selection in that it is not constrained by the structure of the input. Our evidence suggests that the two-choice Stroop effect is caused by this response-based selection mechanism. By contrast, it is known that the flanker effect is determined by the space- and object- based selection mechanisms. We explore whether the conflict resolution of the Stroop and flanker tasks is different as well by embedding these two tasks in a PRP (Psychological Refractory Period) paradigm. We show that the Stroop and the PRP effects are additive whereas the flanker and the PRP effects are underadditive, suggesting that the processes in charge of the conflict resolution in the Stroop and the flanker tasks are indeed different. We discuss possible reasons for this difference, and discuss possible ways in which the response-based mechanism can be implemented in information processing models.