Christophe Tandonnet

Physiological evidence for response inhibition in choice reaction time tasks

Inhibition is a widely used notion proposed to account for data obtained in choice reaction time (RT) tasks. However, this concept is weakly supported by empirical facts. In this paper, we review a series of experiments using Hoffman reflex, transcranial magnetic stimulation and electroencephalography to study inhibition in choice RT tasks. We provide empirical support for the idea that inhibition does occur during choice RT, and the implications of those findings for various classes of choice RT models are discussed.

The influence of time preparation on motor processes assessed by surface Laplacian estimation

OBJECTIVE The present study was aimed at testing whether foreperiod duration affects the activity recorded over the primary sensorimotor cortices during the reaction time. METHODS The foreperiod duration (500 or 2500 ms) was varied across blocks of trials during a between-hand choice reaction time task; surface Laplacians were estimated from EEG recordings by the source derivation method. RESULTS Reaction time was shorter for the 500 ms foreperiod than for the 2500 ms foreperiod. A contralateral negativity/ipsilateral positivity pattern showed up over the primary sensorimotor cortices. The time between the contralateral negativity onset and the electromyographic onset was shorter for the 500 ms foreperiod than for the 2500 ms foreperiod, which suggests that the foreperiod affects the implementation of the motor command. Furthermore, the interval between the onset of the voluntary electromyographic activity and the mechanical response was shorter for the 500 ms foreperiod than for the 2500 ms foreperiod. CONCLUSIONS These results indicate that time preparation affects both central and peripheral motor processes.

Spatial enhancement of EEG traces by surface Laplacian estimation: comparison between local and global methods

OBJECTIVE Surface Laplacian estimation enhances EEG spatial resolution. In this paper, we compare, on empirical grounds, two computationally different estimations of the surface Laplacian. METHODS Surface Laplacian was estimated from the same monopolar data set with both Hjorths method [local; Electroenceph Clin Neurophysiol 39 (1975) 526] as modified by MacKay [Electroenceph Clin Neurophysiol 56 (1983) 696] and with spherical spline interpolation [global; Electroenceph Clin Neurophysiol 72 (1989) 184]. RESULTS The grand averages computed with the two methods proved to be very similar but differed markedly from the monopolar ones. The two different computations were highly correlated, presented low relative errors and allowed to evidence comparable experimental effects. CONCLUSIONS These results suggest that Hjorths method and spherical spline interpolation convey similar topographic and chronometric informations. SIGNIFICANCE We provide empirical evidence that local and global methods of surface Laplacian estimation are equivalent to improve the spatial resolution of EEG traces. Global methods allow to explore the scalp topography and local methods allow to spare time in electrode setting that can be useful for studies on special populations (i.e. children, aged subjects) and for clinical purposes.

Knowing when to respond and the efficiency of the cortical motor command : A laplacian ERP study

The objective was to test whether motor preparation can modulate the efficiency of the cortical motor command. The electroencephalogram (EEG) was recorded from electrodes located over the primary sensorimotor cortices during the performance of a between-hand choice reaction time task in which foreperiod duration (the interval between the warning and the imperative signals, 800 vs. 2800 ms) was varied across blocks of trials. In order to increase the spatial resolution of the EEG traces, surface Laplacian was estimated. The amplitude of the negative wave developing over the hemisphere contralateral to the response was smaller for the short foreperiod associated with the best performance level. These results indicate that the activation of the primary sensorimotor cortex involved in the response is less pronounced for the short foreperiod, suggesting that temporal advance information increases the efficiency of the cortical motor command.

Tactile stimulations and wheel rotation responses: toward augmented lane departure warning systems

When an on-board system detects a drift of a vehicle to the left or to the right, in what way should the information be delivered to the driver? Car manufacturers have so far neglected relevant results from Experimental Psychology and Cognitive Neuroscience. Here we show that this situation possibly led to the sub-optimal design of a lane departure warning system (AFIL, PSA Peugeot Citroën) implemented in commercially available automobile vehicles. Twenty participants performed a two-choice reaction time task in which they were to respond by clockwise or counter-clockwise wheel-rotations to tactile stimulations of their left or right wrist. They performed poorer when responding counter-clockwise to the right vibration and clockwise to the left vibration (incompatible mapping) than when responding according to the reverse (compatible) mapping. This suggests that AFIL implements the worse (incompatible) mapping for the operators. This effect depended on initial practice with the interface. The present research illustrates how basic approaches in Cognitive Science may benefit to Human Factors Engineering and ultimately improve man-machine interfaces and show how initial learning can affect interference effects.

On the reduced influence of contour on saccade metrics and its competition with stimulus size

It is well known that the metrical properties of saccadic eye movements are strongly influenced by the extraction of low-level visual features (e.g., luminance). Higher-level visual features (e.g., contour) also play a role, but their relative contribution and time course remain undetermined. Here, we investigated this issue, by testing the influence of contour on saccade metrics. We used a saccade-targeting task in which a peripheral target was, on some trials, simultaneously displayed with a less eccentric distractor. This paradigm is known to yield a global effect, that is a deviation of the eyes towards an intermediate location between the stimuli. The novelty was to test whether this effect would vary with the alignment of the distractors elementary features. Distractors were of high vs. low luminance, and composed of 16 pixels that were either aligned or misaligned by 0.23° or 0.43°. Our prediction, under the hypothesis that contour intervenes, was that aligned distractors, which formed a definite contour, would deviate the eyes more strongly than misaligned distractors. On the contrary, we found that distractors of high luminance produced greater eye deviations when they were misaligned, and hence more largely spread, than when they were aligned. Furthermore, low-luminance distractors deviated the eyes to the same extent irrespective of their alignment, though showing a reversed, contour-like, effect of alignment for early-triggered saccades. We proposed that contour has only limited influence on saccade metrics, when other, lower-level and more salient visual features, such as the extent of the stimulus pattern, are available.

On the limited effect of stimulus boundaries on saccade metrics

How the endpoint of saccadic eye movements is determined out of many potential peripheral locations is a crucial issue in the field of vision. Models of saccade generation account for this seemingly selective process in terms of competitive interactions between populations of neurons that encode respectively for different saccade amplitudes and directions. However, these models do not specify which visual stimulus properties other than the relative location of the stimuli are involved and how these properties contribute to ultimately determine a single saccade endpoint. We addressed this issue by contrasting the respective contributions of the 2-D spatial extent of the stimuli and the location of their boundaries in a global-effect paradigm. Participants were presented a to-be-looked-at peripheral target stimulus with or without a less eccentric visually invariant distractor. The extent of the target stimulus was manipulated in either one or two dimensions, such that targets differed either by their 2-D spatial extent (small, medium, or large circle) or the location of their boundaries (circle vs. horizontal or vertical ellipse of medium size). Results showed that the distractor deviated the eyes away from the target with the deviation varying with the 2-D spatial extent of the target but not the location of its boundaries. This finding suggests that the spatial distribution of luminance contrast and/or the number of elementary features that compose the stimuli prevails over visual boundaries in specifying the saccade endpoint. Implications for models of saccade generation are discussed.

Limitations of short range Mexican hat connection for driving target selection in a 2D neural field: activity suppression and deviation from input stimuli

Dynamic Neural Field models (DNF) often use a kernel of connection with short range excitation and long range inhibition. This organization has been suggested as a model for brain structures or for artificial systems involved in winner-take-all processes such as saliency localization, perceptual decision or target/action selection. A good example of such a DNF is the superior colliculus (SC), a key structure for eye movements. Recent results suggest that the superficial layers of the SC (SCs) exhibit relatively short range inhibition with a longer time constant than excitation. The aim of the present study was to further examine the properties of a DNF with such an inhibition pattern in the context of target selection. First we tested the effects of stimulus size and shape on when and where self-maintained clusters of firing neurons appeared, using three variants of the model. In each model variant, small stimuli led to rapid formation of a spiking cluster, a range of medium sizes led to the suppression of any activity on the network and hence to no target selection, while larger sizes led to delayed selection of multiple loci. Second, we tested the model with two stimuli separated by a varying distance. Again single, none, or multiple spiking clusters could occur, depending on distance and relative stimulus strength. For short distances, activity attracted toward the strongest stimulus, reminiscent of well-known behavioral data for saccadic eye movements, while for larger distances repulsion away from the second stimulus occurred. All these properties predicted by the model suggest that the SCs, or any other neural structure thought to implement a short range MH, is an imperfect winner-take-all system. Although, those properties call for systematic testing, the discussion gathers neurophysiological and behavioral data suggesting that such properties are indeed present in target selection for saccadic eye movements.