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At least 199 records · Page 11Linked to original sources

PubMed2003

Preparatory states in crossmodal spatial attention: spatial specificity and possible control mechanisms.

We used event-related functional magnetic resonance imaging to study the neural correlates of endogenous spatial attention for vision and touch. We examined activity associated with attention-directing cues (central auditory pure tones), symbolically instructing subjects to attend to one hemifield or the other prior to upcoming stimuli, for a visual or tactile task. In different sessions, subjects discriminated either visual or tactile stimuli at the covertly attended side, during bilateral visuotactile stimulation. To distinguish cue-related preparatory activity from any modulation of stimulus processing, unpredictably on some trials only the auditory cue was presented. The use of attend-vision and attend-touch blocks revealed whether preparatory attentional effects were modality-specific or multimodal. Unimodal effects of spatial attention were found in somatosensory cortex for attention to touch, and in occipital areas for attention to vision, both contralateral to the attended side. Multimodal spatial effects (i.e. effects of attended side irrespective of task-relevant modality) were detected in contralateral intraparietal sulcus, traditionally considered a multimodal brain region; and also in the middle occipital gyrus, an area traditionally considered purely visual. Critically, all these activations were observed even on cue-only trials, when no visual or tactile stimuli were subsequently presented. Endogenous shifts of spatial attention result in changes of brain activity prior to the presentation of target stimulation (baseline shifts). Here, we show for the first time the separable multimodal and unimodal components of such preparatory activations. Additionally, irrespective of the attended side and modality, attention-directing auditory cues activated a network of superior frontal and parietal association areas that may play a role in voluntary control of spatial attention for both vision and touch.

Attention↗

PubMed2003

Tactile dominance in speeded discrimination of textures.

When assessing the roughness of textures, no single sensory modality universally dominates perception. Instead, the task and stimuli critically determine to what extent a given sense is favoured. We report a visuotactile texture assessment experiment, consisting of the speeded discrimination of roughened textile samples, in the presence of a congruent or an incongruent textile distractor. When discriminating between samples, visual assessment of textile roughness was modulated by incongruous tactile distractors, but not vice versa, even when visual distractors were more discriminable than tactile targets. This asymmetry in interference suggests that 'modality appropriateness' is not purely a function of the discriminative ability of a sensory modality, but that ecological validity may play a role in determining the more 'appropriate' sense for a given task. Results are discussed in relation to the claim that the assessment of textiles is more ecologically suited to touch than to vision.

Adult↗

PubMed2003

Absence of cross-modal reorganization in the primary auditory cortex of congenitally deaf cats.

To investigate possible cross-modal reorganization of the primary auditory cortex (field A1) in congenitally deaf cats, after years of auditory deprivation, multiunit activity and local field potentials were recorded in lightly anesthetized animals and compared with responses obtained in hearing cats. Local field potentials were also used for current source-density analyses. For visual stimulation, phase-reversal gratings of three to five different spatial frequencies and three to five different orientations were presented at the point of central vision. Peripheral visual field was tested using hand-held stimuli (light bar-shaped stimulus of different orientations, moved in different directions and flashed) typically used for neurophysiological characterization of visual fields. From 200 multiunit recordings, no response to visual stimuli could be found in A1 of any of the investigated animals. Using the current source-density analysis of local field potentials, no local generators of field potentials could be found within A1, despite of the presence of small local field potentials. No multiunit responses to somatosensory stimulation (whiskers, face, pinna, head, neck, all paws, back, tail) could be obtained. In conclusion, there were no indications for a cross-modal reorganization (visual, somatosensory) of area A1 in congenitally deaf cats.

Animals↗

PubMed2003

Cross-modal congruency and visual capture in a visual elevation-discrimination task.

Participants in this experiment were required to discriminate the elevation of visual target stimuli (upper versus lower) presented to either side of fixation, while simultaneously trying to ignore vibrotactile distracters presented independently from the index finger (up) or thumb (lower) of either hand. The participants' hands were occluded from view under an opaque screen while the visual targets were situated directly over the hands above the screen. Participants responded more slowly on this elevation-discrimination task when the vibrotactile distracters were incongruent with the elevation of the visual targets (i.e. a "lower" vibration to the thumb during the presentation of an upper visual target) than when they were congruent (presumably due to the competing responses primed by the target and distracter stimuli on incongruent trials). The vibrotactile distracters had less of an effect on performance when a pair of rubber hands was placed on top of the screen, "holding" the target lights, in a posture consistent with that of the participant. Those participants who agreed most strongly with a statement about feeling the vibrations at the location of the rubber hands in a post-congruency task questionnaire evidenced the greatest reduction in the magnitude of the cross-modal congruency effect.

Adult↗

PubMed2003

Space-independent modality-driven attentional capture in auditory, tactile and visual systems.

Extending previous evidence for attentional shifts across auditory and visual modalities without the confound of the two modalities originating at different locations (Turatto et al. 2002), we investigated attention shifts between auditory and tactile modalities, and between tactile and visual modalities. Two stimuli (S1 and S2), either in the same or in different modalities, were delivered from the same spatial source and were separated by a variable temporal gap. S1 was task irrelevant, whereas S2 required a speeded discrimination. Results showed that modality switching is detrimental independently of the stimulated modality as long as the temporal lag between S1 and S2 is short enough that there is not time to switch attention before S2 is delivered. We observed automatic, modality-driven, attentional capture, with ipsimodal trials leading to faster response times than crossmodal trials. The present results cannot be accounted for by spatial artifacts, response priming or criterion shifts, and are interpreted as the consequence of a space-independent attentional shift across sensory modalities.

Acoustic Stimulation↗

PubMed2003

Latency and accuracy of saccades to somatosensory targets.

PURPOSE: To examine the accuracy and latency of reflexive saccades to vibratory stimulation of the fingertips made by normal human subjects and to compare the findings to those of visually guided saccades. METHODS: Eye movements were recorded using infrared oculography. Stimuli were presented via an array of audiometric bone vibrator transducers driven at 250 Hz and positioned at eye level in a darkened room. Target locations were at 0 and +/-5, 10, and 15 deg. Visual stimuli were green LEDs. Saccades were analysed interactively off-line and latency and amplitude measured for both types of saccade. RESULTS: Saccades to tactile stimuli had longer latencies and showed less accurate final eye positions than those to equivalent visual targets; they were unaffected by subject age. Error magnitude for the tactile saccades increased monotonically with increasing target eccentricity; because the fingers remained in a fixed position throughout the testing, this also meant that error was lowest for the thumb and increased with progression outwards towards the ring finger. Visually guided refixations were accurate and differed less than 0.2 deg across target locations. Subject age had no effect on performance. CONCLUSIONS: Human subjects may make relatively accurate refixations to tactile targets in the absence of visual cues, but only to certain locations/fingers; others were localised very poorly. Further studies are needed to determine whether finger selection or target location is the primary determinant of accuracy in this task.

Adult↗

PubMed2005

Neuronal activity in primary motor cortex differs when monkeys perform somatosensory and visually guided wrist movements.

This study was designed to investigate how activity patterns of primary motor cortical (MI) neurons change when monkeys perform the same movements guided by somatosensory and/or visual cues. Two adult male rhesus monkeys were trained to make wrist extensions and flexions after holding a steady position during an instructed delay period lasting 0.5-2.0 s. Monkeys held against a 0.07 Nm load that opposed flexion movements. Wrist movements were guided by vibratory cues (VIB-trials), visual cues (VIS-trials), or both in combination (COM-trials). Extracellular recordings of 188 MI neurons were made during all three paradigms. Individual neurons were counted twice, once for each movement direction, yielding 376 cases. All neurons had significant task-related activity (TRA) changes relative to delay period activity during at least one of the three paradigms. TRA was analyzed to determine if it was different as a function of the sensory cue(s) that initiated movement and that specified movement endpoints. Cases were grouped by whether the TRA changes were greater in VIB- or VIS-trials; this defined their "bias". One hundred and eighteen cases (31.4%) had greater TRA changes in VIB-trials (Vb-neurons), whereas 185 (49.2%) showed greater TRA changes in VIS-trials (Vs-neurons). The remaining 73 cases (19.4%) had similar TRA changes in VIB- and VIS-trials (Nb-neurons). For Vb- and Vs-neurons, earlier TRA onsets and greater TRA changes were observed in the trials for which these neurons were biased. During the COM-trials, the TRA was intermediate. During the trials for which the activity was not biased, the TRA was the least. For Nb-neurons, no significant TRA differences were observed across paradigms. TRA changes of MI neurons may represent movement planning-related inputs from other central, presumably cortical, sources as well as contribute to motor outflow from the cortex. These data suggest that Vb- and Vs-neurons are affected differently by somatosensory- and visually related central inputs, resulting in different TRAs, even for essentially identical movements. Such differences may depend not only on the type of sensory information that initiates movement but also whether that information specifies movement endpoints or might interfere with movement monitoring.

Animals↗

PubMed2005

Are somatosensory saccades voluntary or reflexive?

The present study examines whether the distinction between voluntary (endogenous) and reflexive (stimulus-elicited) saccades made in the visual modality can be applied to the somatosensory modality. The behavioural characteristics of putative reflexive pro-saccades and voluntary anti-saccades made to visual and somatosensory stimuli were examined. Both visual and somatosensory pro-saccades had much shorter latency than voluntary anti-saccades made in the direction opposite to a peripheral stimulus. Furthermore, erroneous pro-saccades were made towards both visual and somatosensory stimuli on approximately 11-13% of anti-saccade trials. The observed difference in pro- and anti-saccade latency and the presence of pro-saccade errors in the anti-saccade task indicates that a somatosensory stimulus can elicit a form of reflexive saccade comparable to pro-saccades made in the visual modality. It is proposed that a peripheral somatosensory stimulus can elicit a form of reflexive saccade and that somatosensory saccades do not depend exclusively on higher level endogenous control processes for their generation. However, a comparison of the underlying latency distributions and of peak-velocity profiles of saccades made to visual and somatosensory stimuli showed that this distinction may be less clearly defined for the somatosensory modality and that modality-specific differences (such as differences in neural conduction rates) in the underlying oculomotor structures involved in saccade target selection also need to be considered. It is further suggested that a broader conceptualisation of saccades and saccade programming beyond the simple voluntary and reflexive dichotomy, that takes into account the control processes involved in saccade generation for both modalities, may be required.

Adult↗

PubMed2005

Effects of cold stimulation on secondary hyperalgesia (HA) induced by capsaicin in healthy volunteers.

Little is known about the sensory characteristics and underlying mechanisms behind secondary hyperalgesia (HA) (2 degrees HA). The aim of the present study was to investigate the relationships between two different noxious stimuli, mechanical and cold on capsaicin-induced 2 degrees HA. Fourteen healthy volunteers were exposed to three different cold stimuli (20, 10, 0 degrees C) 30 s each, on both forearms. The cold stimuli were applied before (baseline) and 8 min after intradermal administration of 50-microg capsaicin to the forearm, distally to the injection site in the inspected area of 2 degrees HA. Pain intensities were assessed immediately after each cold stimulus by means of a visual analogue scale (cold-VAS). Additionally, areas of mechanical HA (cm(2)) were assessed distally and proximally to the injection site at three different time points: 5, 8 (right after the second series of cold stimuli), and 30 min after the injection. No significant differences in cold-VAS were found between pre- and post-capsaicin injection at the tested forearm (P= 0.334), whereas significant reduction from pre- to post-injection was found in cold-VAS in the control forearm (P= 0.024). Further, 8 min after the injection, the cold stimulation led to an expansion of 2 degrees HA area (from 5.1+/-1.38 to 11.4+/-1.72 cm(2)) to punctuate stimuli distally but not proximally to the injection site (P<0.05). It is concluded that there is no HA to cold stimuli within the area of mechanical 2 degrees HA. However, cooling acts as a conditioning stimulus and expands the area of capsaicin-induced punctuate HA.

Adult↗

PubMed2005

Hemispheric sensitivity to body stimuli in simple reaction time.

Previous research indicates that people respond fastest when the motor response is (spatially, functionally, anatomically, or otherwise) congruent to the visual stimulus. This effect, called ideomotor compatibility, is thought to be expressed in motor areas. Congruence occurs when the stimulus and response share some dimensions in their internal representations. If the ideomotor compatibility hypothesis were true, we would expect facilitation when right hand stimuli are presented to the left hemisphere, or left hand stimuli are presented to the right hemisphere. To address this issue, we conducted a simple reaction time experiment with lateralized targets. Participants were instructed to press a button as soon as a target was observed. The target stimulus was a left hand, a right hand, or a neutral control. Each hemisphere showed faster responses to contralateral hand stimuli as compared with ipsilateral hand stimuli, consistent with the ideomotor compatibility hypothesis. The results support an automatic and implicit processing of visual stimuli within motor representations even when no recognition of, or decision about, the stimulus is necessary.

Adult↗

PubMed2005

Spatial tuning of tactile attention modulates visual processing within hemifields: an ERP investigation of crossmodal attention.

Recent event-related brain potential (ERP) studies have revealed crossmodal links in spatial attention, but have not yet investigated differences in the spatial tuning of attention between task-relevant and irrelevant modalities. We studied the spatial distribution of attention in vision under conditions where participants were instructed to attend to the left or right-hand in order to detect infrequent targets, and to entirely ignore visual stimuli presented via LEDs at two eccentricities in the left or right hemifield. Hands were located close to two of these four LEDs in different blocks. Visual N1 amplitudes were enhanced when visual stimuli in the cued hemifield were close to the attended hand, relative to visual stimuli presented at the other location on the same side. These within-hemifield attentional modulations of visual processing demonstrate that crossmodal attention is not distributed diffusely across an entire hemifield. The spatial tuning of tactile attention transfers crossmodally to affect vision, consistent with spatial selection at a multimodal level of representation.

Adult↗

PubMed2005

Simultaneity constancy: detecting events with touch and vision.

What are the consequences of visual and tactile neural processing time differences when combining multisensory information about an event on the body's surface? Visual information about such events reaches the brain at a time that is independent of the location of the event. However, tactile information about such events takes different amounts of time to be processed depending on the distance between the stimulated surface and the brain. To investigate the consequences of these differences, we measured reaction times to touches and lights on different parts of the body and the perceived subjective simultaneity (PSS) for various combinations. The PSSs for pairs of stimuli were predicted by the differences in reaction times. When lights and touches were on different body parts (i.e. the hand and foot) a trend towards compensation for any processing time differences was found, such that simultaneity was veridically perceived. When stimuli were both on the foot, subjects perceived simultaneity when the light came on significantly earlier than the touch, despite similar processing times for these stimuli. When the stimuli were both on the hand, however, there was complete compensation for the significant processing time differences between the light and touch such that simultaneity was correctly perceived, a form of simultaneity constancy. To identify if there was a single simultaneity constancy mechanism or multiple parallel mechanisms, we altered the PSS of an auditory-visual stimulus pair and looked for effects on the PSS of a visual-touch pair. After repeated exposure to a light/sound pair with a fixed time lag between them, there was no effect on the PSS of a touch-light pair, suggesting multiple parallel simultaneity constancy mechanisms.

Adult↗

PubMed2005

Visual and haptic representations of scenes are updated with observer movement.

Scene recognition has been found to be sensitive to the orientation of the scene with respect to the stationary observer. Recent studies have shown, however, that observer movement can compensate for changes in visual scene orientation, through a process of spatial updating. Here we investigated whether spatial updating in scene recognition is affected by the encoding or learning modality by examining whether observer movement can also compensate for orientation changes in haptic scene recognition. In experiment 1, we replicated previously reported effects of observer movement on visual scene recognition. In experiment 2, we used the same apparatus as in experiment 1 but here participants were required to learn and recognize the scenes using touch alone. We found a cost in recognition performance with changes in scene orientation relative to the stationary observer. However, when participants could move around the scene to recognize the new orientation, then this cost in recognition performance disappeared. Thus, we found that spatial updating applies to recognition in both the visual and haptic modalities, both of which intrinsically encode the spatial properties of a scene.

Adolescent↗

PubMed2005

Integration of visual and tactile stimuli: top-down influences require time.

In a visuotactile congruency task, a distracting flash of light presented near a tactile target can influence speeded judgments of tactile location. Localization of the tactile target is more rapid when the elevation of the visual distractor is congruent with the tactile stimulus than when it is incongruent. The goal of the present study was to examine the degree of control that can be exerted on the process proposed to integrate the visual and tactile stimuli. To this end, the proportion of spatially congruent items was manipulated across blocks of trials. A robust congruency effect was observed across three experiments. There was no effect of proportion congruency (varied between 75 and 11% congruent) when the visual event was presented only 30 ms prior to the tactile event. When this lead-time was increased to 100 ms there was a significant increase in the congruency effect, for errors, in the high proportion congruent conditions (experiment 3). We conclude that with sufficient lead-time, top-down influence can be exerted in this task, however, when presented at near simultaneity, visuotactile integration is independent of top-down effects.

Adult↗

PubMed2005

Assessing the effect of visual and tactile distractors on the perception of auditory apparent motion.

In this study we investigated the effect of the directional congruency of tactile, visual, or bimodal visuotactile apparent motion distractors on the perception of auditory apparent motion. Participants had to judge the direction in which an auditory apparent motion stream moved (left-to-right or right-to-left) while trying to ignore one of a range of distractor stimuli, including unimodal tactile or visual, bimodal visuotactile, and crossmodal (i.e., composed of one visual and one tactile stimulus) distractors. Significant crossmodal dynamic capture effects (i.e., better performance when the target and distractor stimuli moved in the same direction rather than in opposite directions) were demonstrated in all conditions. Bimodal distractors elicited more crossmodal dynamic capture than unimodal distractors, thus providing the first empirical demonstration of the effect of information presented simultaneously in two irrelevant sensory modalities on the perception of motion in a third (target) sensory modality. The results of a second experiment demonstrated that the capture effect reported in the crossmodal distractor condition was most probably attributable to the combined effect of the individual static distractors (i.e., to ventriloquism) rather than to any emergent property of crossmodal apparent motion.

Acoustic Stimulation↗

PubMed2005

Functional imaging of human crossmodal identification and object recognition.

The perception of objects is a cognitive function of prime importance. In everyday life, object perception benefits from the coordinated interplay of vision, audition, and touch. The different sensory modalities provide both complementary and redundant information about objects, which may improve recognition speed and accuracy in many circumstances. We review crossmodal studies of object recognition in humans that mainly employed functional magnetic resonance imaging (fMRI). These studies show that visual, tactile, and auditory information about objects can activate cortical association areas that were once believed to be modality-specific. Processing converges either in multisensory zones or via direct crossmodal interaction of modality-specific cortices without relay through multisensory regions. We integrate these findings with existing theories about semantic processing and propose a general mechanism for crossmodal object recognition: The recruitment and location of multisensory convergence zones varies depending on the information content and the dominant modality.

Acoustic Stimulation↗

PubMed2006

Subjective somatosensory vertical during dynamic tilt is dependent on task, inertial condition, and multisensory concordance.

To investigate how visual and vestibular cues are integrated for the perception of gravity during passive self-motion, we measured the ability to maintain a handheld object vertical relative to gravity without visual feedback during sinusoidal roll-tilt stimulation. Visual input, either concordant or discordant with actual dynamic roll-tilt, was delivered by a head-mounted display showing the laboratory. The four visual conditions were darkness, visual-vestibular concordance, stationary visual scene, and a visual scene 180 degrees phase-shifted relative to actual tilt. Tilt-indication performance using a solid, cylindrical joystick was better in the presence of concordant visual input relative to the other visual conditions. In addition, we compared performance when indicating the vertical by the joystick or a full glass of water. Subjects indicated the direction of gravity significantly better when holding the full glass of water than the joystick. Matching the inertial characteristics, including fluid properties, of the handheld object to the glass of water did not improve performance. There was no effect of visual input on tilt performance when using the glass of water to indicate gravitational vertical. The gain of object tilt motion did not change with roll-tilt amplitude and frequency (+/-7.5 degrees at 0.25 Hz, +/-10 degrees at 0.16 Hz, and +/-20 degrees at 0.08 Hz), however, the phase of object tilt relative to subject tilt showed significant phase-leads at the highest frequency tested (0.25 Hz). Comparison of the object and visual effects observed suggest that the task-dependent behavior change may be due to an attentional shift and/or shift in strategy.

Attention↗

PubMed2006

A cognitive intersensory interaction mechanism in human postural control.

Human control of upright body posture involves inputs from several senses (visual, vestibular, proprioceptive, somatosensory) and their central interactions. We recently studied visual effects on posture control and their intersensory interactions and found evidence for the existence of an indirect and presumably cognitive mode of interaction, in addition to a direct interaction (we found, e.g., that a 'virtual reality' visual stimulus has a weaker postural effect than a 'real world' scene, because of its illusory character). Here we focus on the presumed cognitive interaction mechanism. We report experiments in healthy subjects and vestibular loss patients. We investigated to what extent a postural response to lateral platform tilt is modulated by tilt of a visual scene in an orthogonal rotational plane (anterior-posterior, a-p, direction). The a-p visual stimulus did not evoke a lateral postural response on its own. But it enhanced the response to the lateral platform tilt (i.e., it increased the evoked body excursion). The effect was related to the velocity of the visual stimulus, showed a threshold at 0.31 degrees /s, and increased monotonically with increasing velocity. These characteristics were similar in normals and patients, but body excursions were larger in patients. In conclusion, the orthogonal stimulus arrangement in our experiments allowed us to selectively assess a cognitive intersensory interaction that upon co-planar stimulation tends to be merged with direct interaction. The observed threshold corresponds to the conscious perceptual detection threshold of the visual motion, which is clearly higher than the visual postural response threshold. This finding is in line with our notion of a cognitive phenomenon. We postulate that the cognitive mechanism in normals interferes with a central visual-vestibular interaction mechanism. This appears to be similar in vestibular loss patients, but patients use less effective somatosensory instead of vestibular anti-gravity mechanisms.

Adult↗