Selective preservation of naming from description and the "restricted preverbal message"

We report the case of a patient, LEW, who presents with modality-specific naming deficits. He is seriously impaired in naming pictures of both objects and actions. His naming to auditory verbal definitions and of actions carried out by the experimenter is, however, relatively well preserved. He has no visual perceptual deficits and his access to the semantics of pictures is as good as that to the semantics of spoken words. While LEW is not an optic aphasic patient, his pattern of performance is relevant to the debate that has taken place of the organization of the semantic system. We discuss his case from this perspective and argue that LEW's selective deficits support the multiple semantics position. We also argue that the "preverbal message" level in the speech production model of Levelt (1989) is the equivalent of "verbal semantics." We provide additional constraints and principles to the concept of the preverbal message and we term the system so constrained the "restricted preverbal message." Copyright 2000 Academic Press.     

Frames of reference in spatial span

In four experiments, a computerized Corsi-like paradigm was used to assess which of the many reference frames are used in visuospatial short-term memory. By varying the relative orientation (slanted +/-45° or in an upright position) of the head and the displays, we modulate the utility of the allocentric, egocentric (eye- and head-centred), and template-centred reference frames. The results of all experiments showed the crucial importance of the gravitational allocentric reference frames while using visuospatial short-term memory to retain a spatial sequence of elements. The results also provide some support for a mental rotation process involved in recognition following angular displacement of a multi-item display.     

Refractoriness and the healthy brain: A behavioural study on semantic access

While many behavioural studies on refractory phenomena in lexical/semantic access have focused on the mechanisms involved in the oral production of names, comprehension tasks have been almost exclusively used in neuropsychological studies on brain damaged patients. We report the results of two experiments on healthy participants conducted by means of speeded word to picture matching tasks. They assess the effects of the same variables examined in the study of refractory access dysphasic patients: semantic distance and word frequency (experiment 1) and presentation rate and serial position effects (experiment 2). Semantic access patients usually show little effect of word frequency but a large semantic distance effect. However, critical in characterising the syndrome as ‘refractory’, effects of presentation rate and serial position should also be present. The experiments involved the use of a deadline response procedure. The critical manipulation was the absence of a Response Stimulus Interval (RSI) in the fast presentation rate conditions; slower presentation rates involved 1 s RSI. With these manipulations the typical behavioural pattern of performance provided by semantic access dysphasic patients was reproduced. Semantic distance effects were more powerful than word frequency effects (experiment1). Presentation rate effects were found and, most important for a “refractory” account of the effects, a serial position effect was obtained (experiment 2). These results provide the first evidence of such a broad range of refractory effects at the same time in comprehension tasks in healthy subjects and support a purely semantic account for the locus of refractoriness. Moreover, error analysis showed a predominance of perseverative errors with subsequent representations of the same target, supporting a failure of cognitive control mechanisms as the cause of refractory behaviour. The findings are discussed in the light of current models of lexical and semantic processing.     

An effect of spatial-temporal association of response codes: understanding the cognitive representations of time

The present study addresses the question of how such an abstract concept as time is represented by our cognitive system. Specifically, the aim was to assess whether temporal information is cognitively represented through left-to-right spatial coordinates, as already shown for other ordered sequences (e.g., numbers). In Experiment 1, the task-relevant information was the temporal duration of a cross. RTs were shorter when short and long durations had to be responded to with left and right hands, respectively, than with the opposite stimulus-response mapping. The possible explanation that the foreperiod effect (i.e., shorter RTs for longer durations) is greater with right than with left hand responses is discarded by results of Experiment 2, in which right and left hand responses alternated block-wise in a variable foreperiod paradigm. Other explanations concerning manual or hemispheric asymmetries may be excluded based on the results of control experiments, which show that the compatibility effect between response side and cross duration occurs for accuracy when responses are given with crossed hands (Experiment 3), and for RTs when responses are given within one hand (Experiment 4). This pattern suggests that elapsing time, similarly to other ordered information, is represented in some circumstances through an internal spatial reference frame, in a way that may influence motor performance. Finally, in Experiment 5, the temporal duration was parametrically varied using different values for each response category (i.e., 3 short and 3 long durations). The compatibility effect between hand and duration was replicated, but followed a rectangular function of the duration. The shape of this function is discussed in relation to the specific task demands.     

Developmental dissociations of preparation over time: deconstructing the variable foreperiod phenomena

In a variable foreperiod (FP) paradigm, reaction times (RTs) decrease as a function of FP on trial n (FP effect) but increase with FP on trial n - 1 (sequential effects). These phenomena have traditionally been ascribed to different strategic preparation processes. According to an alternative explanation, common conditioning laws underlie both effects. The present study aims to disentangle these opposite views using a developmental perspective. In Experiment 1A, 4- to 11-year-old children and a control group of adults performed a simple RT task with variable FPs (1, 3, and 5 s). Furthermore, 12 4- to 5-year-old children were retested after 14 months (Experiment 1B). In Experiment 2, a narrower pool of participants (4, 5, and 6 years old) performed a variable FP paradigm with different FPs (1, 2, and 3 s). The results consistently suggest different ontogenetic time courses for the two effects: The sequential effects are already present in the youngest group (4-5 years old), whereas the FP effect appears gradually some years later. These findings are not fully compatible with previous views. A dual-process account is proposed to explain the data.     

Direct visual access in reading for meaning

Two experiments examined whether phonological receding is an obligatory stage in reading for meaning or whether direct access to a word's semantic representation is the general rule. The first study demonstrated that the time to make a semantic decision about a pair of words was much more delayed by misspelling than was the time to make a phonological one. The second study investigated the effect of varying the syllabic length of a word on reaction time in a category decision task. While reaction time varied with the semantic difficulty of the category decision, it generally proved invariant with respect to syllabic length. It is argued that reading for meaning generally uses a direct route from visual form to semantic representation.     

Attractor dynamics in word recognition: converging evidence from errors by normal subjects, dyslexic patients and a connectionist model

People make both semantic and visual errors when trying to recognise the meaning of degraded words. This result mirrors the finding that deep dyslexic patients make both semantic and visual errors when reading aloud. We link the results with the demonstration that a recurrent connectionist network which produces the meaning of words in response to their spelling pattern produces this distinctive combination of errors both when its input is degraded and when it is lesioned. The reason why the network can simulate the errors of both normal subjects and patients lies in the nature of the attractors which it develops as it learns to map orthography to semantics. The key role of attractor structure in the successful simulation suggests that the normal adult semantic reading route may involve attractor dynamics.     

Connectionist Modelling of Word Recognition

Connectionist models offer concretemechanisms for cognitive processes. When these modelsmimic the performance of human subjects theycan offer insights into the computationswhich might underlie human cognition. We illustratethis with the performance of a recurrentconnectionist network which produces the meaningof words in response to their spellingpattern. It mimics a paradoxical pattern oferrors produced by people trying to read degradedwords. The reason why the network produces thesurprising error pattern lies in the nature ofthe attractors which it develops as it learns tomap spelling patterns to semantics. The keyrole of attractor structure in the successfulsimulation suggests that the normal adult semanticreading route may involve attractor dynamics, andthus the paradoxical error pattern isexplained.     

On the emergence of modern humans

The emergence of modern humans with their extraordinary cognitive capacities is ascribed to a novel type of cognitive computational process (sustained non-routine multi-level operations) required for abstract projectuality, held to be the common denominator of the cognitive capacities specific to modern humans. A brain operation (latching) that allows this novel computational process is proposed as well as a physics-inspired mechanism that could explain its rather recent emergence without invoking unlikely genetic or structural changes.     

Preserved and impaired task-switching abilities in non-demented patients with Parkinson's disease

Existing studies on task switching in Parkinson's disease (PD) patients have led to somewhat different results. In particular, it is unclear whether PD patients have a deficit in attentional control. In this study, we assessed task-switching abilities in samples of non-demented PD patients and elderly controls. We used a paradigm in which there was a random task sequence and the task was cued in every trial. This allowed the investigation of both task-set reconfiguration and task-set dissipation. In terms of the proportion of errors made, the patients showed increased switch cost and congruency effects. For reaction times, PD patients showed enlarged congruency effects on switch trials, specifically in the condition in which we used a short constant response-cue interval (RCI). Nevertheless, in a similar fashion to older controls, the patients showed reductions in reaction time switch cost from a short to a long cue-target interval (CTI) and from a short to a long RCI. While these latter findings, respectively, suggest unimpaired task preparation and task dissipation on correct trials in the PD patients, the overall results show that they have a deficit in biasing and selecting currently relevant task sets and more generally argue in favour of a failure of attentional control in PD.