Hemiface contributions to hemispheric dominance in visual speech perception

Lateralized displays are used widely to investigate hemispheric asymmetry in language perception. However, few studies have used lateralized displays to investigate hemispheric asymmetry in visual speech perception, and those that have yielded mixed results. This issue was investigated in the current study by presenting visual speech to either the left hemisphere (LH) or the right hemisphere (RH) using the face as recorded (normal), a mirror image of the normal face (reversed), and chimeric displays constructed by duplicating and reversing just one hemiface (left or right) to form symmetrical images (left-duplicated, right-duplicated). The projection of displays to each hemisphere was controlled precisely by an automated eye-tracking technique. Visual speech perception showed the same, clear LH advantage for normal and reversed displays, a greater LH advantage for right-duplicated displays, and no hemispheric difference for left-duplicated displays. Of particular note is that perception of LH displays was affected greatly by the presence of right-hemiface information, whereas perception of RH displays was unaffected by changes in hemiface content. Thus, when investigated under precise viewing conditions, the indications are not only that the dominant processes of visual speech perception are located in the LH but that these processes are uniquely sensitive to right-hemiface information.     

Hypothalamic multiunit activity and LH secretion in conscious sheep

Summary The relationship between the pulsatile secretion of luteinizing hormone (LH) and multiunit activity (MUA) in the median eminence and retrochiasmatic area (RCh-ME) of the hypothalamus was investigated within 13 conscious, ovariectomized ewes during the anoestrous season. Eight of the ewes had been treated with oestradiol to reduce their LH pulse frequency. To test whether the activity had been recorded from sites involved in the control of GnRH release, we electrically stimulated the sites studied with the recording electrode and used the LH responses to classify the animals retrospectively for analysis of the MUA data. Following stimulation, LH secretion was either stimulated (Group STIM, n=5 ewes), inhibited (Group INHIB, n=4) or showed no response (Group NR, n=4). Statistical analysis of the MUA data revealed that the onset of LH pulses was associated with an increase in cell activity in STIM ewes and a decrease in activity in both Group INHIB and Group NR ewes. Histological examination revealed that the electrodes were located near the midline in Group STIM ewes, but 1.25 or 2 mm lateral of the midline in Groups NR and INHIB, respectively. We concluded that the MUA in the RCh-ME probably reflects the activity of cells with fibres or terminals involved in the control of GnRH release. Activity which increased at the onset of LH pulses was detected in medial areas of the RCh-ME and may reflect the activity of GnRH neurones. The activity which decreased at the onset of LH pulses in lateral areas of the RCh-ME suggests that both stimulatory and inhibitory inputs may be involved in the release of GnRH pulses.     

Hypothalamic neuron involvement in integration of reward, aversion, and cue signals

The lateral hypothalamus (LHA) is involved in integrative functions related to emotion, reward, aversion, and learning. It is, however, unclear whether the medial forebrain bundle (MFB) forms a substrate common to the anterior and posterior hypothalamic areas or whether information regarding rewarding and aversive stimuli converges on and is integrated by the same hypothalamic neuron. In the present study, unit activity in the LHA and lateral preoptic-anterior hypothalamic area (lPOA-AHA) of the rat was recorded during discrimination learning of cue tone stimuli (CTS) that predicted glucose or intracranial self-stimulation (ICSS) as rewarding stimuli, or electric shock or tail pinch as aversive stimuli, using identical behavior, licking. We examined functional differences between the LHA and lPOA-AHA. In positive reinforcement experiments a rat was rewarded by glucose or ICSS only when it licked a spout presented in front of its mouth. The threshold current for ICSS was used. In negative reinforcement experiments an aversive stimulus, either electric shock or tail pinch was applied if the rat did not lick the spout. The strengths of electric shock and tail pinch were selected to produce an avoidance ratio less than 20-30%, averaged in all trials. The activity of 507 LHA and 249 lPOA-AHA neurons was analyzed during both glucose and ICSS trials. The effects of both glucose and ICSS on the same LHA or lPOA-AHA neuron were usually in the same direction, i.e., either both excitatory or both inhibitory. Of 143 LHA and 44 lPOA-AHA neurons that responded to both rewards, the responses of 117 (81.8%) LHA and 35 (79.5%) lPOA-AHA neurons to both stimuli were similar. The activity of 131 LHA and 153 lPOA-AHA neurons was analyzed in both electric shock and tail pinch trials. The effects of both electric shock and tail pinch on the same LHA or lPOA-AHA neuron were usually in the same direction. Of 29 LHA and 27 lPOA-AHA neurons that responded to both aversive stimuli, the responses of 28 (96.6%) LHA and 25 (92.6%) lPOA-AHA neurons to both were similar. The activity of 170 LHA and 195 lPOA-AHA neurons in response to both rewarding glucose and/or ICSS stimulation and aversive electric shock and/or tail pinch was analyzed. About one-third of the neurons in each area were reward specific (57/170 in LHA; 63/195 in lPOA-AHA), whereas relatively few were aversion specific in each area (21/170 in LHA; 15/195 in lPOA-AHA).(ABSTRACT TRUNCATED AT 400 WORDS)     

What role does multisensory integration play in the visuotactile perception of texture?

Previous research has shown that vision and touch are both effective at many roughness discrimination tasks; however, there is no evidence that using both senses simultaneously improves discrimination performance. We investigated the nature of this failure to integrate multisensory inputs, using three varieties of forced-choice discrimination tasks. In Experiment 1, visual, tactile and bimodal roughness discriminations were made between pairs of fabric stimuli. Bimodal discriminations were typically performed with a sensitivity somewhere between that observed for the unimodal presentations. In Experiment 2, a similar design was used except that during the stimulus presentation, one interval contained a unimodal (vision or touch) stimulus, the other interval a bimodal stimulus presentation. Bias toward the bimodal interval would indicate an increase in the magnitude of perceived roughness for such presentations. No such bias was found. In Experiment 3, participants made single-interval, bimodal discriminations, determining whether a rough stimulus was presented to touch, to vision, to both modalities, or to neither modality. The improved performance seen for the dual-target vs. single-target presentations was best modelled as arising from a trialwise division of attention between vision and touch. Overall, these results suggest that vision and touch act as independent sources of roughness information, where the necessity to divide attention across both modalities reduces the discriminative ability in (or information available from) each of these individual modalities.     

Hypnotizability-related integration of perception and action

Hypnotizability is a cognitive trait able to modulate many behavioural/physiological processes and associated with peculiar functional characteristics of the frontal executive system. This review summarizes experimental results on hypnotizability-related differences in sensorimotor integration at a reflex and an integrated level (postural control) and suggests possible interpretations based on morpho-functional considerations. In particular, hypnotizability-related differences in spinal motoneurones excitability are described, and the role of attention and imagery in maintaining a stable upright stance when sensory information is reduced or altered and when attention is absorbed in cognitive tasks is discussed as a function of hypnotic susceptibility. The projections from prefrontal cortex to spinal motoneurones and the balance between the activation of the right and left cortical hemisphere are considered responsible for the hypnotizability-related modulation of reflex responses, while the differences in postural control between subjects with high (highs) and low (lows) hypnotic susceptibility are considered a possible consequence of the activity of the locus coeruleus, which is also involved in attention, and of the cerebellum, which might be responsible for different internal models of postural control. We suggest a highly pervasive role of hypnotic susceptibility in human behaviour through the modulation of the integration of perception and action, which could be relevant for neurorehabilitative treatments and for the adaptation to special environments.     

Hypnotizability-related integration of perception and action

Hypnotizability is a cognitive trait able to modulate many behavioural/physiological processes and associated with peculiar functional characteristics of the frontal executive system. This review summarizes experimental results on hypnotizability-related differences in sensorimotor integration at a reflex and an integrated level (postural control) and suggests possible interpretations based on morpho-functional considerations. In particular, hypnotizability-related differences in spinal motoneurones excitability are described, and the role of attention and imagery in maintaining a stable upright stance when sensory information is reduced or altered and when attention is absorbed in cognitive tasks is discussed as a function of hypnotic susceptibility. The projections from prefrontal cortex to spinal motoneurones and the balance between the activation of the right and left cortical hemisphere are considered responsible for the hypnotizability-related modulation of reflex responses, while the differences in postural control between subjects with high (highs) and low (lows) hypnotic susceptibility are considered a possible consequence of the activity of the locus coeruleus, which is also involved in attention, and of the cerebellum, which might be responsible for different internal models of postural control. We suggest a highly pervasive role of hypnotic susceptibility in human behaviour through the modulation of the integration of perception and action, which could be relevant for neurorehabilitative treatments and for the adaptation to special environments.     

Left hemispheric dominance of vestibular processing indicates lateralization of cortical functions in rats

Lateralization of cortical functions such as speech dominance, handedness and processing of vestibular information are present not only in humans but also in ontogenetic older species, e.g. rats. In human functional imaging studies, the processing of vestibular information was found to be correlated with the hemispherical dominance as determined by the handedness. It is located mainly within the right hemisphere in right handers and within the left hemisphere in left handers. Since dominance of vestibular processing is unknown in animals, our aim was to study the lateralization of cortical processing in a functional imaging study applying small-animal positron emission tomography (microPET) and galvanic vestibular stimulation in an in vivo rat model. The cortical and subcortical network processing vestibular information could be demonstrated and correlated with data from other animal studies. By calculating a lateralization index as well as flipped region of interest analyses, we found that the vestibular processing in rats follows a strong left hemispheric dominance independent from the “handedness” of the animals. These findings support the idea of an early hemispheric specialization of vestibular cortical functions in ontogenetic older species.     

Auditory dominance over vision in the perception of interval duration

The “ventriloquist effect” refers to the fact that vision usually dominates hearing in spatial localization, and this has been shown to be consistent with optimal integration of visual and auditory signals (Alais and Burr in Curr Biol 14(3):257–262, 2004). For temporal localization, however, auditory stimuli often “capture” visual stimuli, in what has become known as “temporal ventriloquism”. We examined this quantitatively using a bisection task, confirming that sound does tend to dominate the perceived timing of audio-visual stimuli. The dominance was predicted qualitatively by considering the better temporal localization of audition, but the quantitative fit was less than perfect, with more weight being given to audition than predicted from thresholds. As predicted by optimal cue combination, the temporal localization of audio-visual stimuli was better than for either sense alone.     

Re-evaluating split-fovea processing in word recognition: effects of retinal eccentricity on hemispheric dominance

Several studies have claimed that hemispheric asymmetries affect word recognition right up to the point of fixation because each fovea is split precisely at its vertical midline and information presented either side of this midline projects unilaterally to different, contralateral hemispheres. To investigate this claim, four-letter words were presented to the left or right of fixation, either close to fixation entirely in foveal vision (0.15, 0.25, and 0.35 degrees from fixation) or further from fixation entirely in extrafoveal vision (2.00, 2.10, and 2.20 degrees from fixation). Fixation location and stimulus presentation were controlled using an eye-tracker linked to a fixation-contingent display and performance was assessed using a forced-choice task to suppress confounding effects of guesswork. A left hemisphere advantage was observed for words presented in extrafoveal locations but no hemisphere advantage (left or right) was observed for words presented in any foveal location. These findings support the well-established view that words encountered outside foveal vision project to different, contralateral hemispheres but indicate that this division for word recognition occurs only outside the fovea and provide no support for the claim that a functional split in hemispheric processing exists at the point of fixation.     

Functional hemispheric asymmetry in perception of random forms (author's transl)]

2 experiments were conducted in which Ss made the "same-different" judgement with respect to a pair of random forms which were serially presented to the right and the left VF tachistoscopically. In Exp. I, the stimulus materials were random form painted solidly, and in Exp. II they were contour forms. The major results of both experiments were essentially the same. The results indicated that right VF-lead condition produced more errors than the left VF-lead condition, and that the high complexity form group produced more errors than the low complexity form group. The tendency of left VF-lead superiority was more pronounced when the interval between the 2 stimuli was longer. These results suggest the possibility of the right hemisphere's superior function concerning the perception of random forms.     

Left hemispheric lateralization of brain activity during passive rhythm perception in musicians

The nature of hemispheric specialization of brain activity during rhythm processing remains poorly understood. The locus for rhythmic processing has been difficult to identify and there have been several contradictory findings. We therefore used functional magnetic resonance imaging to study passive rhythm perception to investigate the hypotheses that rhythm processing results in left hemispheric lateralization of brain activity and is affected by musical training. Twelve musicians and 12 nonmusicians listened to regular and random rhythmic patterns. Conjunction analysis revealed a shared network of neural structures (bilateral superior temporal areas, left inferior parietal lobule, and right frontal operculum) responsible for rhythm perception independent of musical background. In contrast, random-effects analysis showed greater left lateralization of brain activity in musicians compared to nonmusicians during regular rhythm perception, particularly within the perisylvian cortices (left frontal operculum, superior temporal gyrus, inferior parietal lobule). These results suggest that musical training leads to the employment of left-sided perisylvian brain areas, typically active during language comprehension, during passive rhythm perception.     

Cue integration and the perception of action in intentional binding

‘Intentional binding’ describes the perceived temporal attraction between a voluntary action and its sensory consequence. Binding has been used in health and disease as an indirect measure of awareness of action or agency, that is, the sense that one controls one’s own actions. It has been proposed that binding results from cue integration, in which a voluntary action provides information about the timing of its consequences or vice versa. The perception of the timing of either event is then a weighted average, determined according to the reliability of each of these two cues. Here we tested the contribution of cue integration to the perception of action and its sensory effect in binding, that is, action and tone binding, by manipulating the sensory reliability of the outcome tone. As predicted, when tone reliability was reduced, action binding was diminished and tone binding was increased. However, further analyses showed that cue integration accounted for changes in action binding, but not tone binding. These findings establish a role for cue integration in action binding and support the growing evidence suggesting that action and tone binding are, at least in part, driven by distinct mechanisms.     

Perceptual coupling in rhythmic movement coordination: stable perception leads to stable action

Rhythmic movement coordination exhibits characteristic patterns of stability, specifically that movements at 0 degrees mean relative phase are maximally stable, 180 degrees is stable but less so than 0 degrees, and other coordinations are unstable without training. Recent research has demonstrated a role for perception in creating this pattern; perceptual variability judgments covary with movement variability results. This suggests that the movement results could be due in part to differential perceptual resolution of the target movement coordinations. The current study used a paradigm that enabled simultaneous access to both perception (between-trial) and movement (within-trial) stability measures. A visually specified 0 degrees target mean relative phase enabled participants to produce stable movements when the movements were at a non-0 degrees relationship to the target being tracked. Strong relationships were found between within-trial stability (the traditional movement measure) and between-trial stability (the traditional perceptual judgment measure), suggestive of a role for perception in producing coordination stability phenomena. The stabilization was incomplete, however, indicating that visual perception was not the sole determinant of movement stability. Rhythmic movement coordination is intrinsically a perception/action system.     

Functional hemispheric asymmetries in perception of digit and line orientation orientation (author's transl)]

In Exp. I, right-handed Ss made the "same" or "diffeeent" judgement to paired digits serially presented to the right and left visual field, and exhibited erroneous judgements in the left visual field lead condition. These results suggest the left hemisphere superiority. In Exp. II, the Ss were requested to make the "same" or "different" judgment and to press a key as fast as possible to the paired line orientation. The right visual field lead condition product more errors than the left visual field lead condition. This suggests the right hemisphere superiority. But no difference appeared between both conditions in the reaction time. The opposite hemispheric superiority, found in perceiving verbal and non-verbal materials in the 2 experiments, would be attributed to the basic difference in "perceptual" process.     

On hemispheric specialisation and visual field effects in the perception of print: A comment on Jordan,Patching, and Thomas

Introduction Due to structural characteristics of the visual pathways, stimuli that are presented in the right half of the visual field (RVF) are initially projected to the left cerebral hemisphere, while those presented in the left half of the visual field (LVF) are projected to the right cerebral hemisphere. This anatomical feature has frequently been taken to support the notion that the well-documented RVF advantage in recognising printed words is a reflection of functional differences between the two hemispheres; notably that of the dominance of the left hemisphere for processing language. Word stimuli that are sent straight to the left hemisphere are believed to profit from more efficient processing than those sent initially to the right hemisphere, because the latter stimuli must follow a longer and more noisy pathway before reaching the language-dominant hemisphere. In the work by Jordan, Patching, and Thomas (2003) the above notion is further developed to speculate that the point of entry of visual information into the cortex may determine the procedure that will underlie the ensuing word recognition process: "... the left hemisphere can process words by mapping orthographic information in parallel onto lexical entries whereas the right hemisphere has a more rudimentary process, that can only map orthographic information sequentially" (p. 50).     

On hemispheric specialisation and visual field effects in the perception of print: A comment on Jordan, Patching, and Thomas

Introduction Due to structural characteristics of the visual pathways, stimuli that are presented in the right half of the visual field (RVF) are initially projected to the left cerebral hemisphere, while those presented in the left half of the visual field (LVF) are projected to the right cerebral hemisphere. This anatomical feature has frequently been taken to support the notion that the well-documented RVF advantage in recognising printed words is a reflection of functional differences between the two hemispheres; notably that of the dominance of the left hemisphere for processing language. Word stimuli that are sent straight to the left hemisphere are believed to profit from more efficient processing than those sent initially to the right hemisphere, because the latter stimuli must follow a longer and more noisy pathway before reaching the language-dominant hemisphere. In the work by Jordan, Patching, and Thomas (2003) the above notion is further developed to speculate that the point of entry of visual information into the cortex may determine the procedure that will underlie the ensuing word recognition process: "... the left hemisphere can process words by mapping orthographic information in parallel onto lexical entries whereas the right hemisphere has a more rudimentary process, that can only map orthographic information sequentially" (p. 50).     

The effects of instruction and hand dominance on grip-to-load force coordination in manipulation tasks

The force applied upon a vertically oriented hand-held object could be decomposed into two orthogonal and highly coordinated components: the grip force (GF; the component perpendicular to the hand-object contact area that provides friction) and the load force (LF; the parallel component that can move the object or support the body). The aim of this study was to investigate the underexplored effects of task instruction and hand dominance on GF-LF coordination. Sixteen right-handed subjects performed bimanual manipulation against a horizontally oriented instrumented device under different sets of instructions. The tasks involved exertion of ramp-and-hold or oscillation patterns of LF performed symmetrically with two hands, while the instructions regarding individual actions were either similar (pull with both hands) or dissimilar (pull with one hand and hold with another). The results revealed that the instruction “to pull” leads to higher indices of GF-LF coordination than the instruction “to hold”, as evidenced by a lower GF-LF ratio, higher GF-LF coupling, and higher GF modulation. The only effect of hand dominance was a moderate time lag of GF relative to LF changes observed in the non-dominant hand. We conclude that the instructions could play an important role in GF-LF coordination and, therefore, they should be taken into account when exploring or routinely testing hand function. Additionally, the results suggest that the neural control of GF of the non-dominant hand could involve some feedback mechanisms.     

Body temperature set-point and the conscious perception of skin temperature in obese women

Summary Obese and control women were immersed in a bath of water kept at 37° C. Oral temperature was measured. The subjects left hand was placed outside the bath for the local application of thermal stimuli between 20° and 45° C, subjects reporting the most pleasant temperature. The lower oral temperatures and lower levels of skin temperature rated as pleasant by obese women as compared with women of normal body weight or less suggests that in obesity the setpoint of body temperature is lowered.