Henderikus G. O. M. Smid

Selective response activation can begin before stimulus recognition is complete: a psychophysiological and error analysis of continuous flow

In discussions of process models of human information processing, the continuous flow conception (Eriksen and Schultz 1979) plays a prominent role. A central prediction of this conception is that any information in a display associated with a response activates that response as soon as it becomes available in the perceptual system. If it concerns the correct response channel, then response facilitation occurs. If it concerns the incorrect response channel, then response competition occurs. To assess these mechanisms more directly, we used psychophysiological measures as well as reaction time (RT). We used the latency of the P3 component of the event related brain potential (ERP) as an index of stimulus evaluation duration, the onset of lateralized motor activity derived from the ERP as an index of selective central motor activation, and the onset of electromyographic activity as an index of the start of peripheral motor activation. Subjects were required to respond to target letters that were either flanked by letters that signalled the opposite response (incompatible arrays), by the target itself (compatible arrays), by letters not associated with a response (neutral arrays), or by no other letters (targets alone). Our results replicated the basic findings obtained in this paradigm. RTs to targets alone did not differ from RTs to compatible arrays. The latter were faster than RTs to neutral arrays, which were faster than RTs to incompatible arrays. P3 latencies were longer on incompatible than on neutral trials, and longer on compatible than on target alone trials. Incorrect central response activation on incompatible trials and correct central response activation on compatible trials, both began earlier than on target alone trials. Peripheral responding on both trial types, however, began later than on target alone trials. More incompatible but less compatible trials than neutral ones exhibited incorrect peripheral response activation. Peripheral response execution was faster and more accurate on compatible than on target alone trials, while it was slower and less accurate on incompatible than on neutral trials. These results indicate, that the flankers activated their associated response channel while display evaluation was still going on, and that response facilitation and competition occurred. After applying criteria proposed by Miller (1988), it was concluded that the set of stimulus recognition processes and the set of response activation processes cannot be regarded as independent stages of processing.

A psychophysiological study of the use of partial information in stimulus-response translation

Ss performed a hybrid go/no-go reaction task in which colored letters were assigned in various ways to 4 finger responses, 2 on each hand. In addition to reaction time, psychophysiological measures were used to assess the duration of stimulus identification and the onset of central and peripheral motor activity. The results suggest that response selection can begin on the basis of 1 stimulus dimension (e.g., color), while the other dimension (e.g., letter form) has not yet been identified. Other results are discussed with regard to selection for action (Allport, 1987) and the importance of stimulus-response translation strategies in the use of partial information.

PSYCHOPHYSIOLOGICAL EVIDENCE FOR CONTINUOUS INFORMATION-TRANSMISSION BETWEEN VISUAL-SEARCH AND RESPONSE PROCESSES

This study was designed to test whether information transmission between the perceptual and motor levels occurs continuously or in discrete steps. Ss performed visual search across nontargets that shared visual features with one of two possible targets, each assigned to a different response. In addition to reaction time, psychophysiological measures were used to assess the duration of target search and the onset of central and peripheral motor activity. Nontargets sharing features with a target selectively activated the response associated with that target, even when it was not present in the display. This suggests that information transmission to the motor level can consist of fine-grained visual information and that visual search and response selection occur in parallel.

Mental representations of morphologically complex words: an event-related potential study with adult humans.

Event related brain potentials (ERPs) were recorded from 13 subjects while performing a lexical decision task. Regular and irregular German principles were presented twice (identical repetition) or were primed by their related infinitives (morphological repetition). Regular participles primed by their infinitives displayed ERP waveforms similar to those evoked by identical repetitions, namely a large positivity with an onset latency of about 200 ms. Irregular participles, by contrast, showed no reliable morphological repetition effects. The results are discussed in terms of the controversy between approaches proposing a single representational mechanism for regular and irregular inflection and the dual mechanism account that suggests an associative memory for the storage of irregulars and a rule-based symbolic processor for generating regular forms.

Representations in human visual short-term memory: an event- related brain potential study

Behavioral measures and event-related potentials (ERPs) were recorded from 12 subjects while performing three delayed matching-to-sample tasks. The task instructions indicated whether stimulus locations, shapes or conjunctions of locations and shapes had to be memorized and matched against a probe. Memory load was varied trial-by-trial by cueing one or two of three stimuli for memorization, followed by one probe. ERPs during memorization and probe response times varied as a function of memory load (posterior negative and anterior positive ERP wave), but not between single-feature and conjunction of features, nor was an interaction found between them. The results support and extend hypotheses by Luck and Vogel (Luck, S.J. and Vogel, E.K., The capacity of visual working memory for features and conjunctions. Nature, 390 (1997) 279-281.) that visual short-term memory stores conjunctions of features rather than single features.

Neurocognition and recovery in first episode psychosis

Cognitive functioning has been found to be a predictor of functional outcome of schizophrenia. It is unclear, however, whether clinical recovery can be predicted by scores on specific cognitive domains. The predictive value of specific neurocognitive domains and other clinical variables for symptomatic and functional outcome and clinical recovery after a 2-year follow-up is explored in a group of 51 patients with non-affective first-episode psychosis. A comprehensive neurocognitive battery was administered 18 and 41weeks after inclusion. Other patient characteristics, which were expected to independently predict clinical recovery, were assessed at baseline. Several neurocognitive tests, especially tests measuring speed of processing, and among others, Duration of Untreated Psychosis (DUP), were significant predictors of clinical recovery. Poor neuropsychological performance accurately predicted non-recovery, but improved neuropsychological performance did not accurately predict recovery. This study confirms previous findings of an association between neurocognition and outcome, but the results also suggest that in order to accurately predict recovery, the role of other factors needs to be investigated.

Patients with obsessive-compulsive disorder are impaired in associative learning based on external feedback.

BACKGROUNDnPatients with obsessive-compulsive disorder (OCD) have to repeat their actions before feeling satisfied that the action reached its intended goal. Learning theory predicts that this may be due to a failure in the processing of external feedback.nnnMETHODnWe examined the performance of 29 OCD patients and 28 healthy volunteers on an associative learning task, in which initial learning is based solely on external feedback signals. Feedback valence was manipulated with monetary gains and losses.nnnRESULTSnAs predicted, OCD patients were impaired during initial, external feedback-driven learning but not during later learning stages. The emotional salience of the feedback modulated learning during the initial stage in patients and controls alike. During later learning stages, however, patients approached near-normal performance with rewarding feedback but continued to produce deficient learning with punishing feedback.nnnCONCLUSIONnOCD patients have a fundamental impairment in updating behavior based on the external outcome of their actions, possibly mediated by faulty error signals in response selection processes.

Continued Cannabis Use and Outcome in First-Episode Psychosis : Data From a Randomized, Open-Label, Controlled Trial

OBJECTIVEnCannabis use has been found to increase the risk of psychosis. It is unclear whether, after a first psychotic episode has occurred, continued cannabis use is associated with poor functional outcome of psychosis.nnnMETHODnAs part of a randomized, open-label, controlled trial, the association of cannabis use and measures for psychopathology and social role functioning after 2 years of follow-up and for the recently proposed outcome measures of symptomatic remission, functional remission, and clinical recovery was explored in a group of 124 patients suffering from nonaffective first-episode psychosis (diagnosed according to DSM-IV and included from a catchment area in the Netherlands of 3.1 million inhabitants from October 2001 through December 2002). Other patient characteristics that were expected to be independently associated with outcome, among them alcohol and other drug use, were assessed at baseline.nnnRESULTSnContinued cannabis use was not associated with symptomatic or functional remission or clinical recovery. After 2 years, cannabis use was related to certain aspects of social role functioning (economic and social activities; explained variance 5.6% and 8.4%, respectively) but not to psychopathology (Positive and Negative Syndrome Scale Positive, Negative, or General symptoms).nnnCONCLUSIONSnOur findings support the notion that continued cannabis use after the onset of a first-episode psychosis is correlated with worse social outcome and should be discouraged whenever possible, but its role in outcome is modest in comparison to other factors.nnnTRIAL REGISTRATIONnNederlands Trial Register: http://www.trialregister.nl (ID: NTR 374).

An electrophysiological study of the insertion of overt response choice

Using electrophysiological measures, the authors studied changes in prestimulus state, stimulus identification, and response-related processing when, in a go/no-go task, forced choice between 2 overt go responses was inserted. The authors observed decreased prestimulus motor preparation (electromyogram), no change in stimulus identification time (selection negativity), a minor increase in response selection time (lateralized readiness potential), a large increase in response preparation time (lateralized readiness potential), a minor effect on response execution time (electromyogram), and a decrease in the activation of a response-inhibition process on no-go trials (frontal event-related potential). The existence of the response-inhibition process was verified by the presence of inverted lateralized readiness potentials on no-go trials. Pure insertion of response choice in a task seems impossible because the choice between activation and inhibition (go/no-go) always seems already present.

Quick Minds Slowed Down: Effects of Rotation and Stimulus Category on the Attentional Blink

Background Most people show a remarkable deficit to report the second of two targets when presented in close temporal succession, reflecting an attentional restriction known as the ‘attentional blink’ (AB). However, there are large individual differences in the magnitude of the effect, with some people showing no such attentional restrictions. Methodology/Principal Findings Here we present behavioral and electrophysiological evidence suggesting that these ‘non-blinkers’ can use alphanumeric category information to select targets at an early processing stage. When such information was unavailable and target selection could only be based on information that is processed relatively late (rotation), even non-blinkers show a substantial AB. Electrophysiologically, in non-blinkers this resulted in enhanced distractor-related prefrontal brain activity, as well as delayed target-related occipito-parietal activity (P3). Conclusion/Significance These findings shed new light on possible strategic mechanisms that may underlie individual differences in AB magnitude and provide intriguing clues as to how temporal restrictions as reflected in the AB can be overcome.