Stochastic dynamics of stimulus encoding in schizophrenia: Theory, testing, and application

Cognitive processing among schizophrenia participants, entailing encoding of presenting stimulation into a format facilitating collateral processes (e.g., memory search), is examined in light of stochastic mathematical models of performance. Results implicate additional encoding operations (encoding subprocesses) as the source of schizophrenia encoding-process elongation. Convergent evidence for this inference, including that from auxiliary neuro-connectionist simulations, are brought forth. Developments from initial, fixed-parameter accounts include random-parameter mixtures, and their Bayesian extensions, formally mediating group-level results to assessment of individual performance. Outgrowths bear on model-selection methodology, according to coherence of group-level and individual-level model functioning (in part addressing the issue of “small-trial-sample model testing”); longitudinal monitoring of encoding-specific treatment response; evaluation of treatment-regimen efficacy with respect to encoding efficiency; and specification of times of measurement interest, in fMRI. The symptom significance of encoding elongation, strongly hinted at by model developments, along with a model-endowed window on exacerbating effects of stress, are drawn out.     

Failure of hierarchical conditional rule learning in the pigeon (Columba livia)

Pigeons were trained with a conditional discrimination task in three-key operant chambers. Choosing either the left or right key was followed by food according to combinations of three preceding events: (a) a houselight illumination condition (dark or light), (b) presence or absence of green flashes on the three keys, (c) a color (amber or blue) of the center sample key. With these 2×2×2 event combinations, eight types of correct trials were prepared: (1) dark→no flash→amber→LEFT, (2) dark→no flash→blue→RIGHT, (3) dark→flash→amber→RIGHT, (4) dark→flash→blue→LEFT, (5) light→no flash→amber→RIGHT, (6) light→no flash→blue→LEFT, (7) light→flash→amber→LEFT, and (8) light→flash→blue→RIGHT. Seven of these eight types were used for training of a given bird, and then the remaining trial type was presented as the test. If the birds had learned the conditional structure of the events (the hierarchical switching rule), they would have responded correctly to the test type. However, they chose the opposite side key, suggesting that they had learned cue configuration or multiple rules to solve the task. Accepted after revision: 13 January 2001 Electronic Publication     

Repetition in visual word identification: Benefits and costs

University students performed lexical tasks with visually presented target words after the presentation of an identical or unrelated prime, at short (80–120?ms) or longer (410–710?ms) prime–target stimulus onset asynchronies (SOAs). Experiment 1 showed perceptual identification benefits in vocal responding at a short SOA that were reduced (accuracy) or reversed (latency) at a longer SOA. Experiment 2 showed a transition from a repetition benefit to a cost over 3 SOAs in a target-masked version of the lexical decision task (LDT; target displayed for only 141?ms). In Experiment 3 the repetition cost was replicated at a 530-ms SOA in the LDT with masked targets, but a repetition benefit was observed in the conventional LDT (target displayed until response). The dependence of repetition costs on target masking is more consistent with biases based on episodic confusions than refractoriness of lexical representations.     

The Limits of Attention for Visual Perception and Action in Aging

ABSTRACT

This study aimed to investigate whether aging results in an increased attentional blink effect in older adults as compared to young adults. A rapid serial visual presentation (RSVP) paradigm was employed in which participants were asked to identify two targets (dual-task condition) presented in rapid succession. These targets were separated by various intervals in a stream of stimuli. The performance for identifying the second target was normally diminished as compared to identification of a single-task target. Various combinations of tasks, such as two perceptual tasks or one perceptual and one action task, as well as different types of pointing action, such as pointing to a displaced target, pointing to a stationary target or pointing to a disappeared target, were manipulated in this study to see if aging may further impact these variables. The results of this study showed that in young adults, successful identification of the first target interfered with identifying the second target, as well as the initiation time (action planning) of pointing to the second target. However, identification of the first target did not interfere with pointing movement time and pointing accuracy, even when the target was displaced, which required online control of action. Conversely, for older adults, successful central identification not only interfered with identifying the second target and with the pointing initiation time, but also interfered with pointing movement time for a displaced target. This suggests that older adults seem to be unable to concurrently identify the first target and correct their already-initiated pointing movement compared to young adults.     

Stimulus–response compatibility for mixed mappings and tasks with unique responses

For two stimulus locations mapped to two keypresses, reaction time is shorter when the mapping is compatible than when it is not (the stimulus–response compatibility, SRC, effect). A similar result, called the Simon effect, occurs when stimulus location is irrelevant, and colour is relevant. When compatibly mapped trials are intermixed with incompatibly mapped trials or Simon task trials, the compatibility effect is eliminated, and the Simon effect is influenced by the location mapping. In five experiments, we examined whether similar mixing effects occur when the two spatial mappings or location-relevant and location-irrelevant tasks use distinct keypresses on the left and right hands. Mixing had considerably less influence on the SRC and Simon effects than it does when the intermixed trial types or tasks share the same responses, even though response time was lengthened to a similar extent. Mixing two tasks for which stimulus location was irrelevant yielded no within-task Simon effect, but the effect was also absent when four stimuli were assigned to two responses on a single hand. The relative lack of influence of mixing on the SRC and Simon effects when the tasks have unique responses implies that suppression of direct activation of the corresponding response occurs primarily when the tasks share responses.     

The nucleus basalis and memory codes: auditory cortical plasticity and the induction of specific, associative behavioral memory

Receptive field (RF) plasticity develops in the primary auditory cortex (ACx) when a tone conditioned stimulus (CS) becomes associated with an appetitive or aversive unconditioned stimulus (US). This prototypical stimulus-stimulus (S-S) association is accompanied by shifts of frequency tuning of neurons toward or to the frequency of the CS such that the area of best tuning of the CS frequency is increased in the tonotopic representation of the ACx. RF plasticity has all of the major characteristics of behavioral associative memory: it is highly specific, discriminative, rapidly induced, consolidates (becomes stronger and more specific over hours to days) and can be retained indefinitely (tested to two months). Substitution of nucleus basalis (NB) stimulation for a US induces the same associative RF plasticity, and this requires the engagement of muscarinic receptors in the ACx. Pairing a tone with NB stimulation actually induces specific, associative behavioral memory, as indexed by post-training frequency generalization gradients. The degree of acquired behavioral significance of sounds appears to be encoded by the number of neurons that become retuned in the ACx to that acoustic stimulus, the greater the importance, the greater the number of re-tuned cells. This memory code has recently been supported by direct neurobehavioral tests. In toto, these findings support the view that specific, learned auditory memory content is stored in the ACx, and further that this storage of information during learning and the instantiation of the memory code involves the engagement of the nucleus basalis and its release of acetylcholine into target structures, particularly the cerebral cortex.     

Culture, Health, and Financial Appraisals: Comparison of Worry in Older Japanese Americans and European Americans

There is limited understanding of the potential impact of cultural identification and values on the emotional experiences of older adults. This study considered potential differences in worry based on culture and acculturation type. The study also evaluated differences in worry based on self-appraisals of perceived health and financial status. Sixty-six older community-based Japanese Americans (JAs) and 65 older European Americans (EAs) completed the Penn State Worry Questionnaire (PSWQ) and the Worry Scale–Revised (WSR). Cultural differences were not found. Social desirability scores were elevated, particularly among JAs who had been relocated to internment camps during World War II. Irrespective of cultural status, elevated average daily worry frequency scores and WSR–Health scores were found in the group who perceived their health status to be poor/fair. Irrespective of cultural status, elevated average daily worry frequency scores, PSWQ scores, and WSR–Financial scores were found in the group who perceived their financial status to be poor/fair. Recommendations for using the WSR with older populations are discussed.     

When old and frail is not the same: Dissociating category and stimulus effects in four implicit attitude measurement methods

It is not always clear whether implicit attitude measures assess the attitude towards single stimuli or the attitude towards categories. Nevertheless, this is important to know—both for interpreting implicit attitude effects and for selecting the test that is most appropriate for individual research aims. We investigated this for four implicit measures: the standard Implicit Association Test (IAT), the IAT-recoding free (IAT-RF), and two versions of the Extrinsic Affective Simon Task (EAST, identification (ID)-EAST). Effects in the standard IAT reflect evaluations of categories and single stimuli, whereas the IAT-RF measures attitudes towards categories only. Both versions of the EAST measure evaluations of single stimuli independently from the evaluation of categories. Three different effect sources are distinguished: attitudes towards single stimuli (IAT; EAST and ID-EAST), attitudes towards target categories (IAT and IAT-RF), and processes of recoding (IAT), which do not necessarily reflect attitudes.     

Facilitation of responses by task-irrelevant complex deviant stimuli

Novel stimuli reliably attract attention, suggesting that novelty may disrupt performance when it is task-irrelevant. However, under certain circumstances novel stimuli can also elicit a general alerting response having beneficial effects on performance. In a series of experiments we investigated whether different aspects of novelty – stimulus novelty, contextual novelty, surprise, deviance, and relative complexity – lead to distraction or facilitation. We used a version of the visual oddball paradigm in which participants responded to an occasional auditory target. Participants responded faster to this auditory target when it occurred during the presentation of novel visual stimuli than of standard stimuli, especially at SOAs of 0 and 200 ms (Experiment 1). Facilitation was absent for both infrequent simple deviants and frequent complex images (Experiment 2). However, repeated complex deviant images did facilitate responses to the auditory target at the 200 ms SOA (Experiment 3). These findings suggest that task-irrelevant deviant visual stimuli can facilitate responses to an unrelated auditory target in a short 0–200 millisecond time-window after presentation. This only occurs when the deviant stimuli are complex relative to standard stimuli. We link our findings to the novelty P3, which is generated under the same circumstances, and to the adaptive gain theory of the locus coeruleus–norepinephrine system (Aston-Jones and Cohen, 2005), which may explain the timing of the effects.