Response inhibition in motor and oculomotor conflict tasks: Different mechanisms,different dynamics?

Previous research has shown that the appearance of task-irrelevant abrupt onsets influences saccadic eye movements during visual search and may slow down manual reactions to target stimuli. Analysis of reaction time distributions in the present study offers evidence suggesting that top-down inhibition processes actively suppress oculomotor or motor responses elicited by a salient distractor, in order to resolve the conflict that arises when reflex-like and deliberate responses are in opposition. Twenty-six participants carried out a variation of the oculomotor capture task. They were instructed to respond with either a saccade toward or with a button press at the side of the hemifield in which a target color singleton appeared. A distractor stimulus could appear either in the same or in the opposite hemifield. Delta plots revealed competition between reflex-like and deliberate response activation, and highlighted selective inhibition of automatic responses: While participants generally responded more slowly in incongruent compared to congruent situations, this effect diminished and even reversed in the slowest speed quantiles. These effects were present in both the oculomotor and motor response-mode conditions.     

More learned irrelevance than perseveration errors in rule shifting in healthy subjects

The present experiments examined the extent to which two possible sources of error affect healthy subjects' performance in a rule-shift task. All 115 participants first received a discrimination learning task, in which a pair of different visual stimuli was presented on each trial, one of which had to be identified as 'correct.' Each stimulus varied in two dimensions: a task-relevant and a task-irrelevant dimension. Feedback on correctness was given after each choice. After eight successive correct choices, the nature of the task-relevant dimension changed: the post-shift learning phase. Two types of error can occur in this phase: continued responding to the former relevant, but now irrelevant, dimension, a perseverative error, and non-responding to the former irrelevant, but now relevant, dimension, an error due to learned irrelevance. Different groups received a post-shift task in which none, one, or both of these two types of error could affect performance. The number of incorrect choices in the post-shift phase was significantly affected by learned-irrelevance errors but not by perseverative errors. An associative-learning model incorporating feedback-induced changes in both associative strength and saliency of the elements comprising the stimuli can explain these results.     

Parallel processing across neural systems: implications for a multiple memory system hypothesis

A common conceptualization of the organization of memory systems in brain is that different types of memory are mediated by distinct neural systems. Strong support for this view comes from studies that show double (or triple) dissociations between spatial, response, and emotional memories following selective lesions of hippocampus, striatum, and the amygdala. Here, we examine the extent to which hippocampal and striatal neural activity patterns support the multiple memory systems view. A comparison is made between hippocampal and striatal neural correlates with behavior during asymptotic performance of spatial and response maze tasks. Location- (or place), movement, and reward-specific firing patterns were found in both structures regardless of the task demands. Many, but not all, place fields of hippocampal and striatal neurons were similarly affected by changes in the visual and reward context regardless of the cognitive demands. Also, many, but not all, hippocampal and striatal movement-sensitive neurons showed significant changes in their behavioral correlates after a change in visual context, irrespective of cognitive strategy. Similar partial reorganization was observed following manipulations of the reward condition for cells recorded from both structures, again regardless of task. Assuming that representations that persist across context changes reflect learned information, we make the following conclusions. First, the consistent pattern of partial reorganization supports a view that the analysis of spatial, response, and reinforcement information is accomplished via an error-driven, or match-mismatch, algorithm across neural systems. Second, task-relevant processing occurs continuously within hippocampus and striatum regardless of the cognitive demands of the task. Third, given the high degree of parallel processing across allegedly different memory systems, we propose that different neural systems may effectively compete for control of a behavioral expression system. The strength of the influence of any one neural system on behavioral output is likely modulated by factors such as motivation, experience, or hormone status.     

Coordination of multiple memory systems

On the basis of lesions of different brain areas, several neural systems appear to be important for processing information regarding different types of learning and memory. This paper examines the development of pharmacological and neurochemical approaches to multiple memory systems from past studies of modulation of memory formation. The findings suggest that peripheral neuroendocrine mechanisms that regulate memory processing may target their actions toward those neural systems most engaged in the processing of learning and memory. In addition, measurements of acetylcholine release in different memory systems reveals extensive interactions between memory systems, some cooperative and some competitive. These results imply that many neural systems, often characterized as relatively independent, may in fact interact extensively, blurring the dependencies of different memory tasks on specific neural systems.     

Negative congruence effects in letter and pseudo-letter recognition: the role of similarity and response conflict

Letters and pseudo-letters were presented in three experiments using a sequential same-different task. While first items were always presented in isolation, the second item was either presented in isolation or surrounded by geometrical non-target shapes that could be congruent or incongruent to the target. In two experiments, a physical sameness criterion was used. In Experiment 1, in one condition, different pairs were always distinct in shape, in another they were similar in shape. Negative congruence effects were obtained for different pairs that are similar. In Experiment 2, this effect is replicated within participants. In this experiment, similar and dissimilar stimuli were mixed. The results were explained in terms of the difficulty of responding different to stimuli that are similar in shape: when the second item is surrounded by a congruent shape, the similarity is emphasized, making this response even more difficult. In Experiment 3, the same stimuli were presented using a categorical sameness criterion. This reduces the role of physical similarity and thus eliminates the response conflict. As a result, negative congruence effects were no longer observed. Taken together, the three experiments identify another source of negative congruence effects besides the ones recently reported in the literature.     

Time-Course of Semantic Composition: The Case of Aspectual Coercion

We examine the time-course of semantic structure formation during real-time sentence comprehension. We do this through the lens of aspectual coercion, a semantic combinatorial operation that lacks morpho-syntactic reflections, yet is indispensable for sentence interpretation. We describe two experiments. Experiment 1 replicates the results of a previously published study (Piñango, Zurif, & Jackendoff, Journal of Psycholinguistic Research, 28(4), 395–414 1999) showing that the cost of implementing aspectual coercion is detectable as late as 250 ms after the operation is licensed. Experiment 2 expands the window of observation by revealing that the implementation of aspectual coercion is not detectable immediately upon its being licensed, that is, at the point at which the syntactic representation is assumed to be fully formed. These findings suggest a dissociation in the integration of information, in which semantic composition—even mandatory and automatic semantic composition—takes time to develop after it is syntactically licensed to do so.The research reported here was supported by NIH Grant DC 03660.     

Children with developmental coordination disorder (DCD) and their ability to disengage ongoing attentional focus: more on inhibitory function

Children with developmental coordination disorder (DCD), along with their Control counterparts, completed two endogenous, spatial precue tasks. When the precue arrow was informative (.80) with respect to target location, the spatial precue effect results demonstrated that children with DCD take significantly longer than Control individuals to volitionally disengage (inhibit) attention from an endogenously cued location (i.e., a disengagement inhibition deficit). When the precue was uninformative (.25), we found, contrary to a common assumption, that the precue arrow automatically moved attention in the direction of the arrow, and, in addition, that DCD children may also be less able to inhibit the precued-induced urge to move attention (i.e., an initiation inhibition deficit). This type of inhibitory difficulty was also indicated for manual response inclinations produced on catch trials. Overall, DCD children appeared to have an elevated difficulty suppressing the initiation of incorrect, stimulus-provoked movement urges, be they manual or attention in nature.     

Modality pairing effects and the response selection bottleneck

The present experiment examined the effects of input/output modality pairings on dual-task performance using the psychological refractory period (PRP) procedure. Four groups of participants performed two tasks composed of the same sets of inputs (visual and auditory) and the same sets of outputs (manual and vocal), but with different input/output modality pairings. Whereas modality pairings had only small effects on single-task reaction times, they had large effects on dual-task reaction times. The modality pairing effect cannot stem from differences in the difficulty of stimulus classification or response execution, because these task demands were the same across groups. The effect also does not appear to result from changes in stimulus-response compatibility. The present findings suggest dual-task interference arises not only from postponement of central operations (due to a central bottleneck), but also from a slowing of central operations whose magnitude is sensitive to the input/output modality pairings.     

Response monitoring and expectancy in random serial RT tasks

Two different sequential patterns have been reported in serial reaction-time (RT) tasks with random stimulus sequences, depending on the response-to-stimulus interval (RSI). When RSI is short a first-order repetition effect and a higher order benefit-only pattern are found, and when RSI is long a cost-benefit pattern is observed. In a series of three experiments, we found that the patterns are not unique for spatial dimensions, and that the benefit-only pattern does not appear for irrelevant stimulus features. The cost-benefit pattern, on the other hand, can shift to irrelevant locations, but not to irrelevant colour. Distributional analyses of the sequential effects demonstrate that the first-order repetition effect can be dissociated from the higher order effects. The results are interpreted as support for the role of response monitoring in the development of the benefit-only pattern at short RSI, while the first-order repetition effect is explained as repetition priming. With a long RSI, the cost-benefit pattern is confirmed as a low-level subjective expectancy process, which is primarily controlled by stimulus location. The data clearly strengthen the support for three different processes generating sequential effects in random serial RT tasks.     

Lesions of the ventral hippocampus, but not the dorsal hippocampus, impair conditioned fear expression and inhibitory avoidance on the elevated T-maze

The hippocampus has been suggested to be involved in spatial (or configural) memory and also in the inhibition of certain response or goal alternatives. An increasing number of anatomical, physiological, and behavioral studies indicate that the hippocampus is functionally heterogeneous along the dorsal-ventral axis. Identification of distinct behavioral roles for the dorsal (DH) and ventral (VH) hippocampus may resolve differences between the various theoretical accounts of hippocampal function. The present study examined the effects of electrolytic lesions restricted to the DH or VH on fear-conditioned freezing, passive avoidance on the elevated T-maze (ETM) test of anxiety, and general activity in male Sprague-Dawley (Charles-River derived) albino rats. We found that rats with lesions of the VH, but not DH showed reduced freezing to both context and tone conditioned stimuli (CS). Rats with VH lesions also showed a reduced latency to emerge from the enclosed arm on trials 2 and 3 of the ETM (indicating reduced anxious behavior), while having no effect on the latency to escape from the open arms on trial 4. There were no differences in activity between the groups. These results indicate that the VH and DH are differentially involved in passive avoidance on the ETM and conditioned freezing to context and tone CS. We suggest that the VH may be specifically involved in modulating goal-oriented, defensive behavior expression through hypothalamic and amygdaloid connections.