A computational model of anterior cingulate function in speeded response tasks: effects of frequency,sequence, and conflict

A growing body of evidence from functional neuroimaging and computational modeling studies indicates that the anterior cingulate cortex (ACC) detects the presence of response conflict and conveys this information to other brain regions, enabling subsequent adjustments in cognitive control. The present study examined previous empirical findings of increased ACC for low-frequency stimuli across three distinct speeded response tasks (two-alternative forced choice, go/no-go, and oddball). Simulations conducted in a neural network model incorporating sequential priming mechanisms (developed in Cho et al., 2002) confirmed that a computational measure of response conflict was higher on low-frequency trials across all three tasks. In addition, the model captured detailed aspects of behavioral reaction time and accuracy data, predicted the dynamics of ACC activity related to trial sequence effects, and provided evidence for the functional role of conflict information in performance monitoring and optimization. The results indicate that the conflict-monitoring hypothesis, augmented by mechanisms for encoding stimulus history, can explain key phenomena associated with performance in sequential speeded response tasks.     

Forgetting curves: implications for connectionist models

Forgetting in long-term memory, as measured in a recall or a recognition test, is faster for items encoded more recently than for items encoded earlier. Data on forgetting curves fit a power function well. In contrast, many connectionist models predict either exponential decay or completely flat forgetting curves. This paper suggests a connectionist model to account for power-function forgetting curves by using bounded weights and by generating the learning rates from a monotonically decreasing function. The bounded weights introduce exponential forgetting in each weight and a power-function forgetting results when weights with different learning rates are averaged. It is argued that these assumptions are biologically reasonable. Therefore power-function forgetting curves are a property that may be expected from biological networks. The model has an analytic solution, which is a good approximation of a power function displaced one lag in time. This function fits better than any of the 105 suggested two-parameter forgetting-curve functions when tested on the most precise recognition memory data set collected by. Unlike the power-function normally used, the suggested function is defined at lag zero. Several functions for generating learning rates with a finite integral yield power-function forgetting curves; however, the type of function influences the rate of forgetting. It is shown that power-function forgetting curves cannot be accounted for by variability in performance between subjects because it requires a distribution of performance that is not found in empirical data. An extension of the model accounts for intersecting forgetting curves found in massed and spaced repetitions. The model can also be extended to account for a faster forgetting rate in item recognition (IR) compared to associative recognition in short but not long retention intervals.     

Implicit and explicit alcohol-related cognitions in heavy and light drinkers

Implicit and explicit alcohol-related cognitions were measured in 2 dimensions: positive-negative (valence) and arousal-sedation, with 2 versions of the Implicit Association Test (IAT; A. G. Greenwald, D. E. McGhee, & J. L. Schwartz) and related explicit measures. Heavy drinkers (n = 24) strongly associated alcohol with arousal on the arousal IAT (especially men) and scored higher on explicit arousal expectancies than light drinkers (n = 24). On the valence IAT, both light and heavy drinkers showed strong negative implicit associations with alcohol that contrasted with their positive explicit judgments (heavy drinkers were more positive). Implicit and explicit cognitions uniquely contributed to the prediction of 1-month prospective drinking. Heavy drinkers' implicit arousal associations could reflect the sensitized psychomotor-activating response to drug cues, a motivational mechanism hypothesized to underlie the etiology of addictive behaviors.     

An attempt to discriminate different types of executive functions in the Wisconsin Card Sorting Test

This study examined the roles of the phonological working memory and the central executive in the Wisconsin Card Sorting Test by altering the materials and the procedure of the task and using a dual-task design, in which cognitive abilities of normal participants were manipulated by performance of the secondary tasks selectively taxing the phonological loop or the central executive. The present study used three novel versions of the Wisconsin Card Sorting Test, namely the WCST-4 stimuli, the WCST-12-stimuli, and the WCST-12-stimuli-box, in all of which the participants were given the exact sorting criterion. So the tasks did not involve processes such as maintenance of inferences about the sorting criterion which would require phonological memory load. However, the tasks were assumed to require the executive process of response inhibition. In the WCST-4-stimuli condition no change was made to the WCST materials. In the other two conditions, relying on the assumption that the three-dimensional nature of the cards triggers inappropriate responses, unidimensional stimulus cards were used instead of the four normal three-dimensional WCST stimulus cards. The difference between these two conditions was that, in the WCST-12-stimuli-box condition, boxes were used to conceal the response cards previously sorted. The results supported Dunbar and Sussman's (1995) argument that some executive processes in the Wisconsin Card Sorting Test require the use of phonological store, and the present design was able to differentiate the type of executive functions that do not involve the use of a phonological loop from the ones that do. In addition, the results concerning manipulations of the visual aspects of the Wisconsin Card Sorting Test suggest that the three-dimensional nature of the WCST stimulus cards leads to an increase in the number of inappropriate responses produced with the executive secondary task interference.     

Interaction between transient change in local muscle structure and segmented leg motor responses

We investigated the interaction between transient change in the local structure of gastrocnemius muscle fibers and the segmented leg motor responses elicited by toes-up rotation of the support surface. The gastrocnemius muscle in healthy young subjects underwent a sustained 2-min, isometric stretch (Prestretch group), followed immediately by the rotations. Analysis showed that the prestretch affected the amplitude of the monosynaptic but not the automatic components of the medial gastrocnemius muscle responses (monosynaptic response: 93 +/- 20% of the mean of the last three rotations in the Prestretch group compared to 174 +/- 42% in the Control group; automatic response: 128 +/- 18% in the Prestretch group versus 123 +/- 31% in the Control group). The shortened tibialis anterior muscle response and the onset latencies of responses were not affected by prestretching the gastrocnemius muscle. The prestretch effect on the amplitude of the monosynaptic (mediated by group Ia afferents) but not the automatic gastrocnemius muscle response (mediated by group II afferents) suggests that the automatic component of the muscle response to platform rotations has a stronger supraspinal influence than the monosynaptic response and is thus less affected by local events such as prolonged stretching.     

No evidence for overshadowing or facilitation of spatial pattern learning by visual cues

Two experiments were conducted to examine the effects of redundant and relevant visual cues on spatial pattern learning. Rats searched for hidden food items on the tops of poles that formed a square (Experiment 1) or a checkerboard (Experiment 2) pattern. The experimental groups were trained with visual cues that specified the locations of the baited poles. All groups were tested without visual cues so that any overshadowing or facilitation of spatial pattern learning by visual cues could be detected. Spatial choices were controlled by the spatial pattern and by the visual cues in both experiments. However, there was no evidence of overshadowing or facilitation of spatial pattern learning by visual cues in either experiment. The results are consistent with the idea that the representation of the spatial pattern that guides choices is not controlled by the same learning processes as those that produce associations between visual cues and food locations.     

Automatic mimicry reactions as related to differences in emotional empathy

The hypotheses of this investigation were derived by conceiving of automatic mimicking as a component of emotional empathy. Differences between subjects high and low in emotional empathy were investigated. The parameters compared were facial mimicry reactions, as represented by electromyographic (EMG) activity when subjects were exposed to pictures of angry or happy faces, and the degree of correspondence between subjects' facial EMG reactions and their self-reported feelings. The comparisons were made at different stimulus exposure times in order to elicit reactions at different levels of information processing. The high-empathy subjects were found to have a higher degree of mimicking behavior than the low-empathy subjects, a difference that emerged at short exposure times (17-40 ms) that represented automatic reactions. The low-empathy subjects tended already at short exposure times (17-40 ms) to show inverse zygomaticus muscle reactions, namely "smiling" when exposed to an angry face. The high-empathy group was characterized by a significantly higher correspondence between facial expressions and self-reported feelings. No differences were found between the high- and low-empathy subjects in their verbally reported feelings when presented a happy or an angry face. Thus, the differences between the groups in emotional empathy appeared to be related to differences in automatic somatic reactions to facial stimuli rather than to differences in their conscious interpretation of the emotional situation.     

Effects of speech accents on interpersonal evaluations: implications for counseling practice and research

This article reviews literature from the fields of psycholinguistics, communications, and social psychology that has examined the effects of speech accents (i.e., regional, national, and international variations in same-language use) on interpersonal attitudes, casual attributions, and subsequent behaviors. The authors link selected findings from this literature to the field of counseling to show that these findings can inform service delivery, particularly counseling conducted with ethnic minority and immigrant populations in the United States. Implications for practice and ideas for future research in this area are also discussed.     

Patients with generalized social phobia direct their attention away from faces

The experiment tested whether patients with social phobia direct their attention to or away from faces with a range of emotional expressions. A modified dot probe paradigm (J. Abnorm. Psychol. 95 (1986) 15) measured whether participants attended more to faces or to household objects. Twenty patients with social phobia were faster in identifying the probe when it occurred in the location of the household objects, regardless of whether the facial expressions were positive, neutral, or negative. In contrast, controls did not exhibit an attentional preference. The results are in line with recent theories of social phobia that emphasize the role of reduced processing of external social cues in maintaining social anxiety.