George A. Michael

Ambient odors modulate visual attentional capture

Sudden visual events capture attention involuntarily because they may signal potential threats. Some theoretical accounts consider that the biological significance of these events is established through the limbic structures. Thus, the manipulation of the limbic activity would affect attentional capture. Since these structures are directly linked to the olfactory system, we have tended to modulate their activity with olfactory stimulations. We have examined behavioral performance in a task of attentional capture by luminance under conditions of ambient odors. Our results show that attentional capture is indeed modulated by ambient odors, and that this modulation may depend on the odors properties.

The ventral premotor cortex (vPM) and resistance to interference.

The authors tested a patient suffering from a circumscribed lesion of the right frontal operculum (FO) in 3 experiments of visual attention involving spatial orienting, maintenance of task-relevant priorities, and control of interference from new and old task-irrelevant items. The authors found that spatial orienting and active maintenance of priorities were intact, but there were difficulties in controlling interference from new and old irrelevant items. These results suggest that the FO is necessary for the direct control of interference, but its lesion alone is not enough to disturb spatial orienting processes or active maintenance of task priorities. The authors discuss the results in light of a hybrid cognitive model of attention.

The thalamus interrupts top-down attentional control for permitting exploratory shiftings to sensory signals.

When attention is involuntarily drawn in a direction different to that of the target, slower motor response times are observed (i.e. the meridian effect). Previous data suggested that the thalamus might participate in the generation of visual salience. What may be the role of the thalamus in the capture by luminance transients when attentional control is in action? A single experiment was administrated in a group of ten healthy volunteers as well as in a group of three patients with unilateral thalamic infarcts. Subjects participated in a task where attentional control was interrupted by a distractor. The meridian effect was present only in the performance of the healthy volunteers and when distractors occurred in the ipsilesional (intact) hemifield of the thalamic patients. These results suggest that when an important signal appears during attentional focalization, the thalamus interrupts current focalization and permits the compilation of an attentional program in the midbrain aiming at generating an orienting response towards the source of this signal.

The human pulvinar and attentional processing of visual distractors.

The processing of a target is degraded when noise is present in proximity, and performance increases as the target-noise distance increases. We tested a group of healthy volunteers and a group of patients, who suffered strokes in the posterior thalamus, in a task where the target-noise distance was manipulated. Whilst controls exhibited the expected pattern of results, thalamic patients exhibited little signs of noise interference. Interference occurred when the target-noise distance was 0 degrees (the target and noise were superimposed), but it was absent for distances equal to and bigger than 1 degree. The results suggest that the coarse grain of visual attention reported previously might be due to some aspects of attention processing underlain by the pulvinar and acting to grab the visual context or background of a target.

Cool colors : Color-induced nasal thermal sensations

We asked subjects to sniff a bottle containing distilled water and to say whether they felt a cooling or warming sensation in the nasal cavity. Odorless food coloring was added to three of these bottles so as to obtain one yellow, one green, one red and one colorless solution. Subjects were presented with each bottle four times under free viewing conditions or while blindfolded, and each nostril was tested separately. Although no thermal stimulus was present, subjects reported thermal sensations, but only under free viewing conditions. The nature of these sensations depended on the color of the solution, with green inducing cooling and red warming sensations. It also depended on which nostril was tested, with warming sensations evidenced only when the left nostril was tested, and cooling sensations only when the right nostril was tested. It is the first time color has been reported to induce nasal thermal sensations in the absence of thermal stimuli. These results are therefore entirely new. Furthermore, they suggest that thermosensory processing and judgment may depend on lateralized processes in the human brain.

The human pulvinar and stimulus-driven attentional control.

The present study compared the behavioral effects of sudden motion onsets or color changes (i.e., featural changes) with the effects of new objects (i.e., multiple changes). Experiments 1 and 2 showed that lesions of the pulvinar affect stimulus-driven attentional control only when it is triggered by featural changes, but not by new objects. Experiment 3 revealed that when appended on a new object, a featural change is processed as a part of a more massive new object: Its attentional effects are larger and remain undisturbed by lesions of the pulvinar. In Experiment 4 a temporal superiority effect was found for featural changes, but not for new objects in healthy subjects. These results suggest that featural changes and new objects may be processed through different pathways and that the pulvinar may be particularly involved in stimulus-driven attentional control by sudden events entailing featural changes.

The tickly homunculus and the origins of spontaneous sensations arising on the hands

Everyone has felt those tingling, tickly sensations occurring spontaneously all over the body in the absence of stimuli. But does anyone know where they come from? Here, right-handed subjects were asked to focus on one hand while looking at it (convergent focusing) and while looking away (divergent focusing) and subsequently to map and describe the spatial and qualitative attributes of sensations arising spontaneously. The spatial distribution of spontaneous sensations followed a proximo-distal gradient, similar to the one previously described for the density of receptive units. The intensity and spatial extent of the reported sensations were modulated by the focusing condition, especially in respect of the left hand. Convergent focusing acted upon the conscious perception of sensations by enhancing or suppressing them. To our knowledge, this is the first ever study of spontaneous sensations, and it offers considerable insight into their sources. The presence of the proximo-distal distributional gradient is a clear sign that receptive units are involved. The enhancement/suppression effects also confirm the involvement of attention. Finally, left-hand dominance suggests several right-hemisphere processes may be involved, such as spatial and tactile perception, and probably interoception.

Impaired emotional memory enhancement on recognition of pictorial stimuli in Alzheimer's disease: No influence of the nature of encoding.

OBJECTIVES There is some discrepancy in the results regarding emotional enhancement of memory (EEM) in Alzheimers disease (AD). Some studies report better retrieval of emotional information, especially positive, than neutral information. This observation is similar to the positivity effect reported in healthy older adults. It was suggested that this effect is due to privileged, deeper and more controlled processing of positive information. One way of testing this is to control both the intention to encode the information and the cognitive resources involved during encoding. Studies investigating EEM in AD patients did not systematically control the nature of encoding. Consequently, the purpose of our study was to examine EEM in AD while manipulating the nature of encoding. METHODS Two experiments were conducted. In Experiment 1 the intention to encode stimuli was manipulated by giving or not giving instructions to participants about the subsequent retrieval. In Experiment 2 cognitive resources involved during encoding were varied (low vs high). In both experiments participants performed immediate recognition task of negative, positive and neutral pictures. 41 mild AD patients and 44 older healthy adults participated in Exp. 1, and 17 mild AD patients and 20 older healthy adults participated in Exp. 2. RESULTS AD patients did not present EEM. Positivity effect, better performance for positive than neutral and negative pictures was observed with older healthy adults. CONCLUSION The data suggest that EEM is disturbed in mild AD patients, with respect to both negative and positive stimuli, at least concerning laboratory, not real-life material. They also suggest there is a positivity effect in healthy older adults and lend support to the idea that this effect is due to preferential cognitive processing of positive information in this population.

Interacting effects of vision and attention in perceiving spontaneous sensations arising on the hands

Visual input and attention enhance tactile perception. But do they influence the perception of spontaneous sensations (SPS) arising in the absence of any external stimulus? We have investigated this by requiring subject to focus attention on each hand while orienting overtly toward it (convergent focusing) or away (divergent focusing) and to subsequently describe the properties of the SPS they felt. Subjects performed this task under free viewing conditions or while blindfolded. Enhanced perception of SPS was found under convergent focusing and also under free viewing conditions. However, the effects of focusing were different whether visual input was available or not. When visual input was available, SPS were enhanced in the fingers but suppressed in the palm, suggesting that enhancement and suppression operated to refine perception of SPS. When visual input was unavailable, only enhancement was observed, even in areas of the hand where suppressing effects were found under free viewing conditions. These interacting effects between vision and attention were observed exclusively in the left hand. A control experiment failed to evidence whether looking at different parts of the hand modulates SPS. We suggest that vision facilitates perception and, when interacting with attention, it enables better perception by promoting suppression of SPS arising in areas of lower sensitivity that may interfere with processing in more sensitive zones. The results are discussed with respect to mechanisms lateralized in the right cerebral hemisphere, and a role of SPS in the maintenance of a conscious image of the body is suggested.

Attentional capture in schizophrenia: failure to resist interference from motion signals.

Introduction. Patients with schizophrenia show high susceptibility to distraction but the neural mechanisms underlying sensitivity to distraction are not clearly established. We designed a paradigm to assess whether sensitivity to distraction and dorsal stream dysfunction are related in schizophrenia. Method. 60 patients, 37 schizotypals, and 58 healthy controls were asked to locate a target square appearing above or below fixation and to ignore a distractor that either moved abruptly (in Experiments 1 and 3) or changed in colour (in Experiment 2). The distractor condition was compared to a baseline condition with no distractor. Resistance to interference was assessed by manipulating the probability of the distractor changing more frequently (50%, 75%, 100%) on one side of fixation. Results. Patients, schizotypals, and controls showed attentional capture with longer response times when the distractor changed as compared to the baseline condition. In contrast to controls, the magnitude of interference from distractors remained stable for patients and schizotypals across all probability conditions and this was confined to attentional capture by motion, not by colour. Conclusion. We found a similar pattern of results in patients and in schizotypals. Our attentional capture paradigm could help to identify early cognitive impairments in populations at risk to develop schizophrenia. The data are interpreted in terms of dysfunction of frontal control on dorsal stream functions in schizophrenia.