Eric Soetens

Control Over Location-Based Response Activation in the Simon Task: Behavioral and Electrophysiological Evidence

In 4 Simon experiments the authors examined control over 2 routes of sensorimotor processing: response priming in the unconditional route and response selection via the conditional route. The Simon effect diminished as the frequency of noncorresponding trials increased. Location-based response priming was observed only when the stimulus followed a corresponding event but not after a noncorresponding trial. Therefore, the unconditional route appears to be suppressed whenever the task context indicates priming as potentially disadvantageous. Moreover, the task-irrelevant stimulus location was used for response selection as a function of correspondence probability. Although exact repetitions of stimulus-response sequences caused a marked speed-up of responses, this 3rd mechanism is independent of unconditional route suppression and frequency-based adjustments in the conditional route.

Expectancy or automatic facilitation? Separating sequential effects in two-choice reaction time.

Two concepts have been proposed to explain sequential effects in serial reaction time, namely, automatic facilitation and subjective expectancy. The present study clarifies the relation between these concepts and specific data patterns obtained in a two-choice task. The proposed repetition-alternation function is particularly suited to distinguish the benefit-only pattern of automatic facilitation from the cost-benefit pattern of expectancy in higher order sequential effects. The data indicate that facilitation and expectancy are independent mechanisms that react in a different way to manipulations of response-stimulus interval, compatibility, and practice. It is suggested that facilitation effects are decaying memory traces related to the structural pathway of the reaction process, whereas expectancy effects are functional and only intervening in the information flow when enough time is available.

Psychophysiological investigation of vigilance decrement: Boredom or cognitive fatigue?

The vigilance decrement has been described as a slowing in reaction times or an increase in error rates as an effect of time-on-task during tedious monitoring tasks. This decrement has been alternatively ascribed to either withdrawal of the supervisory attentional system, due to underarousal caused by the insufficient workload, or to a decreased attentional capacity and thus the impossibility to sustain mental effort. Furthermore, it has previously been reported that controlled processing is the locus of the vigilance decrement. This study aimed at answering three questions, to better define sustained attention. First, is endogenous attention more vulnerable to time-on-task than exogenous attention? Second, do measures of autonomic arousal provide evidence to support the underload vs overload hypothesis? And third, do these measures show a different effect for endogenous and exogenous attention? We applied a cued (valid vs invalid) conjunction search task, and ECG and respiration recordings were used to compute sympathetic (normalized low frequency power) and parasympathetic tone (respiratory sinus arrhythmia, RSA). Behavioural results showed a dual effect of time-on-task: the usually described vigilance decrement, expressed as increased reaction times (RTs) after 30 min for both conditions; and a higher cost in RTs after invalid cues for the endogenous condition only, appearing after 60 min. Physiological results clearly support the underload hypothesis to subtend the vigilance decrement, since heart period and RSA increased over time-on-task. There was no physiological difference between the endogenous and exogenous conditions. Subjective experience of participants was more compatible with boredom than with high mental effort.

Effect of amphetamine on long-term retention of verbal material

A series of five experiments was conducted to investigate the temporal aspects of human memory consolidation of symbolic material through the administration of amphetamine. Subjects had to recall or recognise unrelated words from a previously presented list. The first experiments support the conjecture, based on animal studies, that amphetamine enhances long-term memory performance. Subsequently, enhancement is demonstrated with oral administration before learning, as well as with intramuscular injection after learning. It is shown that improved recall cannot be explained solely by general arousal or attentional processes, but must be due to consolidation. By introducing different test delays we show that consolidation of symbolic material can be modulated by amphetamine during the 1st hour after learning. In a final experiment we demonstrate that the memory enhancement applies to recall as well as to recognition. The implications of the present results are discussed in the context of recent research on LTP processes.

Amphetamine enhances human-memory consolidation

Although it is generally accepted that CNS stimulants have enhancing effects on long-term storage processes in laboratory animals, little is known about their influence on human learning. We report a series of experiments with free recall of lists of unrelated words, demonstrating a significant enhancement on long-term retention after amphetamine administration. A gradual increase of recall was observed up to 1 h after learning, remaining stable for at least 3 days, after oral administration before learning as well as intramuscular injection after learning. The results show that research on humans with drug-induced memory-enhancement techniques is necessary to supplement the animal studies for the understanding of the mechanisms involved in information consolidation.

Freezing of Gait in Parkinson Disease Is Associated With Impaired Conflict Resolution

Background. Freezing of gait (FOG) in Parkinson disease (PD) may involve executive dysfunction. This study examined whether executive functioning and attention are more affected in patients with FOG compared with those without and determined whether these processes are influenced by anti-Parkinson medication. Methods. A total of 11 PD patients with FOG, 11 without FOG, and 10 healthy control subjects, matched for age, gender, and education, participated. General motor, mental and cognitive screening tests, as well as specific neuropsychological assessment of executive functions and the Attention Network Test (ANT) were administered. The ANT was conducted in both ON and OFF phases in a counterbalanced design to determine medication-specific effects. Results. FOG showed a clear association with impairment in the executive control network for conflict resolution (inhibition of unwanted responses and impaired response selection), compared with nonfreezers and healthy controls, F(2, 28) = 5.41, P = .01. Orienting and alerting function did not differ between groups, F < 1. Other executive functions, such as abstract problem solving and mental flexibility were not associated with FOG (P > .10). Anti-Parkinson medication did not ameliorate conflict resolution (P > .10), although orienting attention improved with medication, F(1, 17) = 9.81, P < .01. Conclusions. This study shows an association between impaired conflict resolution and FOG, important in understanding the interplay between cognitive and motor problems, which can lead to specific rehabilitation strategies.

Freezing of gait in Parkinson's disease: disturbances in automaticity and control

Recent studies emphasize a key role of controlled operations, such as set-shifting and inhibition, in the occurrence of freezing of gait (FOG) in Parkinsons disease (PD). However, FOG can also be characterized as a de-automatization disorder, showing impairments in both the execution and acquisition of automaticity. The observed deficits in automaticity and executive functioning indicate that both processes are malfunctioning in freezers. Therefore, to explain FOG from a cognitive-based perspective, we present a model describing the pathways involved in automatic and controlled processes prior to a FOG episode. Crucially, we focus on disturbances in automaticity and control, regulated by the frontostriatal circuitry. In complex situations, non-freezing PD patients may compensate for deficits in automaticity by switching to increased cognitive control. However, as both automatic and controlled processes are more severely impaired in freezers, this hampers cognitive compensation in FOG, resulting in a potential breakdown. Future directions for cognitive rehabilitation are proposed, based on the cognitive model we put forward.

Automatic aftereffects in two-choice reaction time: a mathematical representation of some concepts.

A mathematical model is developed to describe sequential effects in two-choice reaction time experiments with a short response-stimulus interval. Evidence is briefly discussed that in conditions with short response-stimulus intervals, automatic aftereffects dominate sequential effects, and the influence of subjective expectancy can be neglected. In these conditions the model premises three components of automatic aftereffects--facilitation, inhibition, and noise, with a common decay factor. Influence of response-stimulus interval and practice on sequential effects are examined and related to parameter changes in the proposed single-decay model. The decrease of automatic aftereffects with increasing response-stimulus interval is primarily ascribed to an increasing decay factor. The parameter representation of the model also clarifies the issue of the disappearance of automatic aftereffects with practice. It shows a gradual fading of inhibition in the initial stages of practice, together with a slower decrease of the facilitation effect. The single-decay model provides a satisfactory explanation for the processes involved in compatible two-choice reaction time with short response-stimulus interval.

The role of response selection in sequence learning

We investigated the role of response selection in sequence learning in the serial reaction time (SRT) task, by manipulating stimulus–response compatibility. Under conditions in which other types of learning, like perceptual, response-based, and response-effect learning, were unaffected, sequence learning was better with an incompatible than with a compatible stimulus–response mapping. Stimulus discriminability, on the other hand, had no influence on the amount of sequence learning. This indicates that the compatibility effects cannot be accounted for by a different level of task difficulty. Relating our results to the dimensional overlap model (Kornblum, Hasbroucq, & Osman, 1990), which assumes that incompatible stimulus–response mappings require more controlled response selection than do compatible stimulus–response mapping, we suggest that sequence learning in the SRT task is particularly effective when response selection occurs in a controlled way.

Covert signs of expectancy in serial reaction time tasks revealed by event-related potentials.

Choice reaction time is strongly determined by the sequence of preceding stimuli. With long response-stimulus intervals (RSIs), a cost-benefit pattern is observed, which has been related to expectancy, whereas with short RSIs a benefit-only pattern emerges, possibly because of automatic facilitation. In the present study, event-related potentials were recorded while subjects performed serial choice responses to visual and auditory stimuli at long and short RSIs. As expected, reaction times displayedcost-benefit andbenefit-only patterns at long and short RSIs, respectively. In contrast, sequential effects in event-related potential amplitudes displayed a cost-benefit pattern, unaffected by the RSI. The results demonstrate that an expectancy-like mechanism is always active in serial tasks but appears to influence performance only when the RSI is long.