Interval timing as an emergent learning property

Interval timing in operant conditioning is the learned covariation of a temporal dependent measure such as wait time with a temporal independent variable such as fixed-interval duration. The dominant theories of interval timing all incorporate an explicit internal clock, or "pacemaker," despite its lack of independent evidence. The authors propose an alternative, pacemaker-free view that demonstrates that temporal discrimination can be explained by using only 2 assumptions: (a) variation and selection of responses through competition between reinforced behavior and all other, elicited, behaviors and (b) modulation of the strength of response competition by the memory for recent reinforcement. The model departs radically from existing timing models: It shows that temporal learning can emerge from a simple dynamic process that lacks a periodic time reference such as a pacemaker.     

Are Individuals Always Aware of Their Trauma-Related Intrusive Thoughts? A Study of Meta-Awareness

Individuals are not always aware of their mental content. We tested whether lack of awareness occurs in those who have experienced trauma, with and without posttraumatic stress disorder (PTSD). We also examined the role of proposed cognitive mechanisms (working memory and inhibition) in explaining unnoticed intrusions. Individuals with PTSD (n = 44), and varying levels of symptoms (high posttraumatic stress [PTS]: n = 24; low PTS: n = 37) reported on intrusive thoughts throughout a reading task. Intermittently, participants responded to probes about whether their thoughts were trauma related. Participants were “caught” engaging in unreported trauma-related thoughts (unnoticed intrusions) for between 24 and 27% of the probes in the PTSD and high PTS groups, compared with 15% of occasions in the low PTS group. For trauma-related intrusions only, participants lacked meta-awareness for almost 40% of probes in the PTSD group, which was significantly less than that observed in the other groups (～60%). Contrary to predictions, working memory and response inhibition did not predict unnoticed intrusions. The results suggest that individuals who have experienced significant trauma can lack awareness about the frequency of their trauma-related thoughts. Further research is warranted to identify the mechanisms underpinning the occurrence of unnoticed intrusions.     

Developmental prosopagnosia: a study of three patients

We studied perception in three patients with prosopagnosia of childhood onset. All had trouble with other 'within-category' judgments. All were deficient on face matching tests and severely impaired on tests of perception of the spatial relations of facial features and abstract designs, indicating a deficit in the encoding of coordinate relationships, similar to adult-onset prosopagnosia with lesions of the fusiform face area. Two had difficulty perceiving feature colour, which correlated with reduced luminance sensitivity. In contrast to adult-onset patients, saturation discrimination was spared in two and spatial resolution impaired in two. Curvature discrimination was relatively spared. Contrast sensitivity showed variable reductions at different spatial frequencies. We conclude that developmental prosopagnosia is similar to the adult-onset form in encoding deficits for the spatial arrangement of facial elements. Deficits in luminance perception and spatial resolution are more associated with defective encoding for basic object-level recognition, as shown on tests of object and spatial perception.     

Cognitive behaviour therapy of acute stress disorder: a four-year follow-up

The aim of this study was to index the long-term benefits of early provision of cognitive behavior therapy to trauma survivors with acute stress disorder. Civilian trauma survivors (n = 80) with acute stress disorder were randomly allocated to either cognitive behavior therapy (CBT) or supportive counseling (SC) - 69 completed treatment, and 41 were assessed four years post-treatment for post-traumatic stress disorder (PTSD) with the Clinician Administered PTSD Scale. Two CBT patients (8%) and four SC patients (25%) met PTSD criteria at four-year follow-up. Patients who received CBT reported less intense PTSD symptoms, and particularly less frequent and less avoidance symptoms, than patients who received SC. These findings suggest that early provision of CBT in the initial month after trauma has long-term benefits for people who are at risk of developing PTSD.     

Children's working-memory processes: a response-timing analysis

Recall response durations were used to clarify processing in working-memory tasks. Experiment 1 examined children's performance in reading span, a task in which sentences were processed and the final word of each sentence was retained for subsequent recall. Experiment 2 examined the development of listening-, counting-, and digit-span task performance. Responses were much longer in the reading-and listening-span tasks than in the other span tasks, suggesting that participants in sentence-based span tasks take time to retrieve the semantic or linguistic structure as cues to recall of the sentence-final words. Response durations in working-memory tasks helped to predict academic skill and achievement, largely separate from the contributions of the memory spans themselves. Response durations thus are important in the interpretation of span task performance.     

Differential effects of forward or simultaneous conditioned stimulus-unconditioned stimulus intervals on the defensive behavior system of the Norway rat (Rattus norvegicus)

To test several predictions derived from a behavior-systems approach, the authors assessed Pavlovian fear conditioning in rats after 30 trials of forward, simultaneous, or unpaired training. Direct evidence of conditioned fear was collected through observation of flight and freezing reactions during presentations of the conditioned stimulus (CS) alone. The authors also tested the CS's potential to reinforce an instrumental escape response in an escape-from-fear paradigm. On the one hand, rats that received forward training showed conditioned freezing, but no conditioned flight was observed. On the other hand, rats that received simultaneous training showed conditioned flight, but no conditioned freezing was observed. Rats that received either forward or simultaneous pairings showed instrumental learning of the escape-from-fear response. Implications for several theories of Pavlovian conditioning are discussed.     

Patterns of Preference for Numerical and Verbal Probabilities

We report results of an experiment designed to test a principle formulated by Budescu and Wallsten (1995), that, when communicating uncertainty information, mode choices are sensitive to sources and degrees of vagueness. In addition, we examined subjects’ efficacy in using such uncertainty information as a function of communication mode, source, and vagueness. In phase one of the experiment, subjects in a dyad used precise (numerical) or imprecise (verbal) expressions to communicate to a remote partner precise or vague uncertainty about the likelihoods of events. Spinner outcomes were used to generate precise uncertainty while answers to almanac questions were used to elicit vague uncertainty. In phase two, subjects saw the events paired with their partners’ estimates of similar events, and were asked to gamble on one event from each pair. Communication mode preferences were measured as the relative frequency that subjects chose the numerical mode to either express or receive uncertainty information regarding the events. Efficacy was measured as the relative frequency that subjects choose from the pair the event associated with the objectively more probable uncertainty expression. Underlying uncertainty interacted with direction of communication to affect preferences for modes of expression of the probabilities. Subjects preferred precise (numerical) information, especially for precise events (spinners). For vague events (questions), their preference for precise (numerical) information was stronger when receiving than when communicating information. Similar preferences were reflected in the efficiency of subsequent gamble decisions based on the probability estimates. Specifically, decisions were more efficacious (i.e. consistent with Expected Utility) when degrees of precision in events and estimates matched. © 1997 by John Wiley & Sons, Ltd.