Biomedical subjects

L J Fuentes

Publications and source records attributed to L J Fuentes.

11 recordsLinked to original sources

PubMed2001

Inhibition of return in aging and Alzheimer's disease: performance as a function of task demands and stimulus timing.

Inhibition of return (IOR) is a phenomenon of spatial attention that biases attention toward novel events in the environment. Recent evidence suggests that the magnitude and timing of IOR varies as a function of task conditions (e.g., detection vs. discrimination tasks, short vs. long cue-target intervals, intrinsic vs. extrinsic cues). Although IOR appears relatively preserved with both normal aging and Alzheimer's disease (AD), it has been tested under relatively simple task conditions. To test whether IOR is resistant to age and / or AD when cognitive demands are increased, we employed a double-cue IOR paradigm that required categorization as well as detection responses. The stimulus onset asynchrony (SOA) between the cue and target events was varied to determine whether group differences existed in IOR effects over time. Younger normal adults and older normal adults exhibited significant IOR effects on both the detection task and the categorization task at a short cue-target SOA (950 ms). In contrast, AD patients exhibited significant IOR effects at the short SOA on the detection task but not on the categorization task. From the short to the long SOA (3500 ms), IOR effects exhibited by younger normal adults declined significantly during both the detection and the categorization tasks, suggesting that inhibition resolved over time. In contrast, neither older normal adults nor AD patients exhibited SOA-related IOR reductions on the detection task. These results suggest that IOR may show differential age- and AD-related vulnerabilities depending on task conditions and timing characteristics.

Adult↗

PubMed2001

Stroop interference is affected in inhibition of return.

In previous research, we have shown that the processing of targets that are presented to locations subject to inhibition of return (IOR) is affected by an inhibitory tagging mechanism. This mechanism acts by disconnecting activated representations of stimuli at inhibited locations from their associated responses. In two experiments, we assessed whether this inhibitory tagging mechanism of visual attention is also applied to task-irrelevant but prepotent dimensions of target stimuli, such as words in the Stroop task. To test this hypothesis, we examined the Stroop effect in an IOR procedure. The results showed that (1) IOR can be found in a color discrimination task, (2) the Stroop interference was reduced (Experiment 1) or eliminated (Experiment 2) when stimuli appeared at cued locations, as compared with cases in which they were presented at uncued locations, and (3) the effect of inhibitory tagging was limited to the shortest stimulus onset asynchrony value, replicating previous findings. These results agree with the idea that inhibitory tagging, occurring in IOR, affects the efficiency with which color words compete for responses in Stroop-like situations.

Attention↗

PubMed2000

Word-based grouping affects the prime-task effect on semantic priming.

Semantic priming between words is reduced or eliminated if a low-level task such as letter search is performed on the prime word (the prime task effect), a finding used to question the automaticity of semantic processing of words. This idea is critically examined in 3 experiments with a new design that allows the search target to occur both inside and outside the prime word. The new design produces the prime task effect (Experiment 1) but shows semantic negative priming when the target letter occurs outside the prime word (Experiments 2 and 3). It is proposed that semantic activation and priming are dissociable and that inhibition and word-based grouping are responsible for reduction of semantic priming in the prime task effect.

Adult↗

PubMed2000

Semantic priming in the prime task effect: evidence of automatic semantic processing of distractors.

The automaticity of the semantic processing of words has been questioned because of the reduction of semantic priming when the prime word is processed nonsemantically--for example, in letter search (the prime task effect). In two experiments, prime distractor words produced semantic priming in a subsequent lexical decision task, but with the direction of priming (positive or negative) depending on the prime task. Lexico-semantic tasks produced negative semantic priming, whereas letter search produced positive semantic priming. These results are discussed in terms of task-based inhibition. We argue that, given the results from the distractors, the absence of semantic priming does not indicate an absence of semantic activation but reflects the action of control processes on prepotent responses when less practiced responses are needed.

Adult↗

PubMed2000

Inhibitory tagging in inhibition of return is affected in schizophrenia: evidence from the stroop task.

L. J. Fuentes, A. B. Vivas, and G. W. Humphreys (1999b) showed that stimulus processing is affected when stimuli are presented to locations subject to inhibition of return. They argued that activated representations of stimuli presented at inhibited locations are disconnected from their associated responses through an "inhibitory tagging" mechanism occurring in inhibition of return. In the present research, the authors asked whether such a mechanism is affected in people with schizophrenia. Healthy adults and patients with schizophrenia performed a Stroop task in an inhibition of return paradigm. Healthy adults showed a reduction in the Stroop interference when stimuli were presented at inhibited locations, a result that agrees with the inhibitory tagging mechanism hypothesis and replicates previous findings. However, patients with schizophrenia did not show such a reduction, a result suggesting that they have a deficit in inhibitory processing occurring in inhibition of return.

Adult↗

PubMed1999

Inhibitory processing in visuospatial attention in healthy adults and schizophrenic patients.

This study assessed visuospatial attention in healthy adults and medicated schizophrenic patients. Participants performed a visual orientation task in which a peripheral cue was followed. at different intervals, by a target presented either at valid or invalid locations. When the long stimulus onset asynchrony (SOA) was used, participants were presented with either a single peripheral cue (single-cue condition) or two cues, the peripheral cue followed by a central cue (the double-cue condition). Healthy adults showed marginal facilitation effects with the short SOA and similar inhibition of return effects with the long SOA in both single-cue and double-cue conditions. Schizophrenic individuals showed a big facilitation effect with the short SOA and normal inhibition of return with the long SOA in both cue conditions. Results with the short SOA replicated previous findings (Huey, E.D., Wexler, B.E., 1994. Schizophrenia Research 14, 57-63) but, in contrast, we did not observe blunted inhibition of return with the long SOA. An inspection of the differences in the procedures used in both studies may help both to account for the discrepancies and to reveal what processes involved in visuospatial attention are affected in schizophrenia.

Adult↗

PubMed1999

Spatial and semantic inhibitory processing in schizophrenia.

Two experiments assessed inhibitory mechanisms associated with the posterior and anterior attention networks in schizophrenia. Experiment 1 assessed the inhibition of return effect of the posterior network. Both healthy adults and schizophrenic adults showed inhibition of return, suggesting that this inhibitory mechanism of visual orienting is preserved in schizophrenia. Experiment 2 assessed semantic inhibition, which supposedly taps the anterior network, in a lexical-decision task. Healthy adults showed semantic inhibition effects in both visual fields. Schizophrenic adults showed semantic inhibition effects when targets were presented to the left visual field, involving the right hemisphere. However, semantic facilitation rather than inhibition was observed when targets were presented to the right visual field, involving the left hemisphere. These results reflect left hemisphere dysfunction associated with deficits in attentional control in schizophrenia.

Adult↗

PubMed1998

Object-based perceptual grouping affects negative priming.

In 5 experiments the authors examine the role of object-based grouping on negative priming. The experiments used a letter-matching task with multiple letters presented in temporally separated prime and probe displays. On mismatch trials, distractor letters in primes were repeated as targets in probes, or distractor and target letters were completely different. Negative priming was shown by slowed responses when distractors were repeated as targets relative to when the stimuli differed. This occurred both when only letters were presented (Experiments 1 and 4) and when letters were surrounded by boxes (Experiment 5). Experiments 2, 3, and 4 showed that negative priming was affected by the grouping of target and distractor letters in prime displays. Negative priming was reduced when 1 of the distractor letters was placed in the target box and 1 was left outside the box; facilitatory priming was observed when both distractor letters appeared in the target box. The data were accounted for in terms of there being (a) object-based competition for visual selection, (b) inhibition of distractor objects that compete for selection with target objects, and (c) activation or inhibition of the identities of all component elements within target or distractor objects.

Adult↗

PubMed1993

Facilitation and interference effects in a Stroop-like task: evidence in favor of semantic processing of parafoveally-presented stimuli.

In this study we used a modified Stroop word-color task in which the target was a centrally fixated color frame and the distractor was an incompatible, compatible or non-color word. In Experiment 1 distractors were located either within (the inside condition) or outside the frame, at distances of 1.3 deg (near-outside condition) or 2 deg (far-outside condition). In Experiment 2 only the inside and the far conditions were used. The stimuli were on the screen for 150 msec (Experiment 1) or 50 msec (Experiment 2). A non-distractor condition was also included. In Experiment 1, incompatible distractors interfered with naming target colors, and this effect disappeared when the distractor was located far from the target. However, facilitation from compatible distractors was reliable in the farther location. These results were replicated in Experiment 2. The data suggest that (1) unattended items are processed semantically; (2) that facilitation and interference from words in color naming tasks can be caused by different mechanisms; and (3) that distractors are processed differently according to whether they are near or far from fixation.

Adolescent↗

PubMedDate not supplied

[Selective attention deficit in schizophrenia].

OBJECTIVE: To evaluate the cognitive deficits which have been linked with schizophrenia, particularly those related to selective attention from a neurocognitive point of view. DEVELOPMENT: We present a concept of attention consistent with a system of control of information processing composed of a group of neurone networks which carry out specific functions. Some functions are related to visual orientation, while others are involved in executive functions which are at the root of many cognitive skills. The convergence of data from behaviour studies and those made available by neuroimaging techniques have facilitated the identification of neuroanatomical areas responsible for these functions. Thus, the posterior parietal lobe, superior colliculus and pulvinar nucleus of the thalamus are responsible for directing visual attention to different spatial locations. The singular cortex, parts of the medial prefrontal area and supplementary motor area will be involved in executive functions. The question arises as to whether schizophrenia is related to a general attention deficit or to specific deficits linked to the different attention neurone networks. In the studies reviewed attention tasks for the evaluation of facilitatory and inhibitory functions related to the different attention networks were used. CONCLUSIONS: The studies showed that schizophrenic patients present deficits in inhibitory mechanisms which depend on the executive attention network. These results may contribute to a better understanding of the cognitive problems which occur in schizophrenia and also to design more effective strategies for the treatment of this disorder.

Attention↗

PubMedDate not supplied

[Cerebral mechanisms of mathematical thinking].

OBJECTIVE: To suggest a cerebral map of elementary mathematical thinking, and integrate the most relevant findings from neuropsychology with those from cerebral imaging techniques and cognitive behavior experiments. DEVELOPMENT: Firstly we describe investigations into our numerical sense and the way in which numerical information is represented in the human brain. Then, using a multidisciplinary approach, we present the results of different studies of Gerstmann's syndrome, regarding the relation between numerical ability and other cognitive skills; the different participation of the cerebral hemispheres and the special implication of the parietal lobe in mathematical tasks. CONCLUSIONS: Different cerebral regions are involved in doing mental arithmetic, however simple. This makes one think more in terms of cerebral circuits than in a phrenological idea which would assign the responsibility for arithmetical calculations to a specific region. The similarity between the results analysed leads us to the conclusion that one region is particularly involved in understanding numbers, namely the inferior part of the parietal lobe. Different neuronal circuits are used depending on the type of task to be performed. Finally we describe the most relevant models for the processing of numbers which have been developed during the study.

Brain↗