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Biomedical subjects

Bruno Laeng

Publications and source records attributed to Bruno Laeng.

14 recordsLinked to original sources
PubMed2006

Remembering 1500 pictures: the right hemisphere remembers better than the left.

We hypothesized that the right hemisphere would be superior to the left hemisphere in remembering having seen a specific picture before, given its superiority in perceptually encoding specific aspects of visual form. A large set of pictures (N=1500) of animals, human faces, artifacts, landscapes, and art paintings were shown for 2s in central vision, or tachistoscopically (for 100ms) in each half visual field, to normal participants who were then tested 1-6 days later for their recognition. Images that were presented initially to the right hemisphere were better recognized than those presented to the left hemisphere. These results, obtained with participants with intact brains, large number of stimuli, and long retention delays, are consistent with previously described hemispheric differences in the memory of split-brain patients.

Adolescent↗
PubMed2006

Neural control of playing a reversed piano: empirical evidence for an unusual cortical organization of musical functions.

Using functional magnetic imaging techniques and neuropsychological tests, we studied a young male musician (C.S.) who performs at a professional level both on a regular piano keyboard and on a reverse keyboard (reversed right to left). The participant was left-handed, had left dominance for language but, remarkably, right dominance for the control of piano playing on both keyboards. With respect to music perception, C.S. showed left-sided activation dominance within the left superior temporal sulcus, which is normally associated with higher order auditory processing and right-sided activations in the secondary sensory cortex extending into the supramarginal gyrus. We suggest that C.S.'s pattern of functional asymmetry, characterized by audio-motor control using a right-sided network, could be a factor in his exceptional piano-playing ability on both the standard and reversed keyboard.

Adult↗
PubMed2006

The time course of spatial memory processing in the two hemispheres.

Previous studies have shown that memories for positions are often distorted in systematic ways, indicating the influence of categorical positions codes which can bias responses in object-relocation tasks towards stored spatial prototypes. In the present study, we examined the time course of these categorical influences. Subjects had to relocate the position of a tachistoscopically presented dot within a circle, which could appear in either the left visual field (i.e. initially to the right hemisphere) or the right visual field (i.e. initially to the left hemisphere). Three retention intervals between presentation and relocation were used: 500, 2000 and 5000 ms. Performance was most accurate with left visual field/right hemisphere presentation. Systematic distortions were found for angular errors (dot relocations regressed towards the 45 degrees with a quadrant) as well as for radial errors (dots were replaced in the direction of the circle's circumference, and this more so when the dot was further away from the circumference). Importantly, these categorical biases became stronger with retention interval and initial left hemispheric processing. These results suggest that categorical spatial coding might be the default manner in which spatial information is remembered over time. Finally, the left hemisphere may play an important role for such a categorical spatial coding.

Adult↗
PubMed2006

Constructional apraxia after left or right unilateral stroke.

The present study re-assesses the question whether deficits, after brain damage, in constructional tasks can be partitioned in different types of disorders of spatial cognition. Based on a current cognitive neuroscience account, originally proposed by Kosslyn [Kosslyn, S. M. (1987). Seeing and imagining in the cerebral hemispheres: A computational approach. Psychological Review, 94, 148-175], that posits two complementary lateralized systems for the encoding of (categorical and coordinate) spatial relations, it is here proposed that two qualitatively different types of "constructional apraxia" can occur and that the nature of the constructional impairment after unilateral lesions closely reflects the loss of lateralized components for the perceptual processing of differing types of spatial relations. New evidence is presented, based on the study of two groups of patients with unilateral posterior brain lesions, which supports such a bipartition of constructional apraxia. In addition, past evidence is reviewed in the light of this new cognitive neuroscience account.

Aged↗
PubMed2006

Pupillometry of grapheme-color synaesthesia.

Pupil diameters of color-grapheme synaesthetes were measured with an infrared eye-tracker while Stroop-like alphanumeric symbols were passively viewed. Pupils dilated more when synaesthetes viewed incongruently-colored symbols than congruently-colored symbols or symbols printed in the standard black ink. The results show that the physiological measure of pupillary diameter can be used as a marker of the synaesthetic experience.

Adult↗
PubMed2006

Drawing on either side of the brain.

Although both the cerebral laterality of processing visual information and human drawing skill have long been sources of investigation, there is not much empirical work combining the two. In this study, an attempt was made to explore if known different specialisations of the two cerebral hemispheres could help in predicting qualities of drawings produced by each hand. For this purpose, an amateur artist who is able to draw with either the left or the right hand produced a series of realistic drawings of 3D objects. Then 28 participants rated the drawings for several predetermined perceptual and aesthetic properties. The participants judged drawings made with the left hand as superior to those made with the right hand. Given that the right hemisphere controls the left hand, we suggest that this hand might also benefit from the more direct access to lateralised areas that are involved in the processing aspects of visual information and spatial properties (e.g., depth and shading). These perceptual processes may thus play an important role in the ability to draw realistic depictions of objects.

Adolescent↗
PubMed2005

The visual basis of category effects in object identification: evidence from the visual hemifield paradigm.

The basis for the category specific living things advantage in object recognition (i.e., faster and more accurate identification of living compared to nonliving things) was investigated in two experiments. It was hypothesised that the global shape of living things on average provides more information about their basic level identity than the global shape of nonliving things. In two experiments subjects performed name-picture or picture-name verification tasks, in which blurred or clear images of living and nonliving things were presented in either the right or the left visual hemifield. With blurred images, recognition performance was worst for nonliving things presented to the right visual field/left hemisphere, indicating that the lack of visual detail in the stimulus combined with a left hemisphere bias toward processing high frequency visual elements proved detrimental for processing nonliving stimuli in this condition. In addition, an overall living things advantage was observed in both experiments. This advantage was considerably larger with blurred images than with clear. These results are compatible with the global shape hypothesis and converge with evidence using other paradigms.

Adult↗
PubMed2005

Reduced Stroop interference for opponent colors may be due to input factors: evidence from individual differences and a neural network simulation.

Sensory or input factors can influence the strength of interference in the classic Stroop color-word task. Specifically, in a single-trial computerized version of the Stroop task, when color-word pairs were incongruent, opponent color pairs (e.g., the word BLUE in yellow) showed reduced Stroop interference compared with nonopponent color pairs (e.g., BLUE in red). In addition, participants' color discrimination ability was measured by standard color vision tests (i.e., Farnsworth-Munsell 100-Hue Test and Ishihara plates). Error rates in the Farnsworth-Munsell test correlated positively with the amount of Stroop interference. Neural network simulations (variants of J. D. Cohen, K. Dunbar, & J. L. McClelland's, 1990, model) showed that only a distributed trichromatic input layer was able to simulate these findings. Thus, sensory input from the color system needs to be incorporated into current accounts of the Stroop effect.

Adult↗
PubMed2004

Does color synesthesia pose a paradox for early-selection theories of attention?

P.M. is a synesthete who experiences colors when viewing alphanumeric symbols. Her search for a target differing from distractors by a synesthetic color feature takes the form of a pop-out search. Thus, it would seem that synesthesia can occur preattentively. However, discrepancies between the regression functions of response times observed in target-present trials and target-absent trials, and the fact that fast response times occur only when the target is within a few degrees of visual angle from fixation, indicate that P.M.'s synesthesia does not occur preattentively, but rather is within the focus of attention. We conclude that synesthesia is a genuine perceptual phenomenon that can have substantial influence on visual processing.

Attention↗
PubMed2003

Do separate processes identify objects as exemplars versus members of basic-level categories? Evidence from hemispheric specialization.

When an object is identified as a specific exemplar, is it analyzed differently than when it is identified at the basic level? On the basis of a previous theory, we predicted that the left hemisphere (LH) is specialized for classifying objects at the basic level and the right hemisphere (RH) is specialized for classifying objects as specific exemplars. To test this prediction, participants were asked to view lateralized pictures of animals, artifacts, and faces of famous people; immediately after each picture was presented, a label was read aloud by the computer, and the participants decided whether the label was correct for that picture. A label could name the object at either the basic level (e.g., bird) or as an exemplar (e.g., robin). As predicted, we found that basic-level labels were matched faster when pictures were presented in the right visual field (and hence encoded initially in the LH), whereas exemplar labels were matched faster when pictures were presented in the left visual field (and hence encoded initially in the RH).

Adult↗
PubMed2002

Multiple reference frames in neglect? An investigation of the object-centred frame and the dissociation between "near" and "far" from the body by use of a mirror.

In this single case study of a man (AE) who suffered a right hemisphere stroke we showed the co-existence of neglect within different spatial frames: (a) In left hemispace and (b) in 'far' versus 'near' space, both as defined from the patient's viewpoint, as well as (c) for the left side of an object (as defined from an object-centred view). In the experiment, AE's latencies to name the colour of two cubes, each located in one hemispace, were measured. In some conditions, the cubes were placed on a table but in other conditions each cube was held in one hand of an experimenter who could either face the patient or show the cubes while her back was turned towards him. One prediction was that AE would show longer latencies for cubes in left hemispace; however, if object-centred neglect also occurred, then latencies should be even longer for cubes held in the experimenter's left hand. In order to reveal the presence of neglect for 'far' versus 'near' space, the cubes could also be positioned either near to (i.e. reaching distance) or far from the patient (i.e., several metres out of reach), by moving the table or the experimenter. Finally, in some conditions, AE looked at the cubes into a mirror that was positioned far away from his body. Because external objects seen in a mirror can be 'near' the patient's body, the patient actually looked at a 'far' location (i.e. the surface of the mirror) to see an object that is 'near'. The experiment confirmed the presence of all forms of neglect, since AE not only named the colour of a cube seen in his left hemispace more slowly than in right hemispace, but latencies increased for a cube held by the experimenter in her left hand and in left hemispace (both when the left hand was seen directly or as a mirror reflection). Finally, AE's performance was worse for 'far' than 'near' locations, when the cubes were physically located near his body (i.e., within "grasping" space) but seen in the mirror.

Analysis of Variance↗
PubMed2002

Fast responses to neglected targets in visual search reflect pre-attentive processes: an exploration of response times in visual neglect.

AE is a patient who suffered a right hemisphere stroke resulting in visual neglect symptoms. In the first experiment, AE neglected a single visual target that was present in half of the trials and appeared in variable and unpredictable positions on the computer screen. The contrast of the target to the screen's background was also varied. AE demonstrated severe neglect for left-sided targets, and yet his RTs to targets reported incorrectly as absent were faster than correct rejections and even right-sided hits. AEs fast "neglect" responses seem to indicate that the target was detected but that he remained unaware of its presence. Counter intuitively, his fast misses got faster as the discriminability of the target decreased. The possibility that fast responses to neglected targets reflected a guessing strategy, used proportionally to the degree of uncertainty of a target presence, was examined. AEs fast misses were indeed faster at lower level of contrast of the stimulus, but his error rate did not tend to approach the chance level as the guessing model would predict. In a second experiment, AE searched for the letter Z, present on half of the trials, among variable sets of distractor letters. In one condition the distractors were all O's and therefore differed from the target by an elementary feature. In the other condition, the distractors were various letters that differed from the target by combinations of features. The key finding was that fast responses to neglected targets occurred only in the simple feature search task and not in the complex features (conjunction) task. We interpret these findings as indicating that AEs pre-attentive processing can detect pop-out targets on the left-hand side, but that the attentional search is faulty and is aborted early. Hence, the patient's attentional system has an "early start" when "pop-out" forms are present, but can also fail to "grab" the detected target; consequently, by not attending to a stimulus, the patient remains unaware of its presence and will quickly respond "no" to present targets.

Attention↗