Bimodal Stimulation Research Articles

Modified prenatal sensory stimulation influences postnatal behavioral and perceptual responsiveness in bobwhite quail chicks (Colinus virginianus).

Asynchronous bimodal stimulation during prenatal development elicits higher levels of behavioral and physiological arousal in precocial avian embryos than does unimodal sensory stimulation. To investigate whether the increased arousal associated with prenatal bimodal stimulation has enduring effects into postnatal development, bobwhite quail (Colinus virginianus) embryos received no supplemental stimulation, unimodal auditory stimulation, or bimodal (audiovisual) stimulation prior to hatching. Embryos exposed to concurrent bimodal stimulation demonstrated greater levels of behavioral activity and failed to use maternal visual cues to successfully direct species-specific perceptual preferences following hatching. These results provide initial evidence that asynchronous bimodal sensory stimulation during prenatal development can have enduring effects on early postnatal behavioral arousal and perceptual responsiveness and suggest that developmental limitations on prenatal sensory stimulation play an important role in the emergence of species-typical behavior.

Spatial and temporal factors during processing of audiovisual speech: a PET study

Speech perception can use not only auditory signals, but also visual information from seeing the speaker's mouth. The relative timing and relative location of auditory and visual inputs are both known to influence crossmodal integration psychologically, but previous imaging studies of audiovisual speech focused primarily on just temporal aspects. Here we used Positron Emission Tomography (PET) during audiovisual speech processing to study how temporal and spatial factors might jointly affect brain activations. In agreement with previous work, synchronous versus asynchronous audiovisual speech yielded increased activity in multisensory association areas (e.g., superior temporal sulcus [STS]), plus in some unimodal visual areas. Our orthogonal manipulation of relative stimulus position (auditory and visual stimuli presented at same location vs. opposite sides) and stimulus synchrony showed that (i) ventral occipital areas and superior temporal sulcus were unaffected by relative location; (ii) lateral and dorsal occipital areas were selectively activated for synchronous bimodal stimulation at the same external location; (iii) right inferior parietal lobule was activated for synchronous auditory and visual stimuli at different locations, that is, in the condition classically associated with the ‘ventriloquism effect’ (shift of perceived auditory position toward the visual location). Thus, different brain regions are involved in different aspects of audiovisual integration. While ventral areas appear more affected by audiovisual synchrony (which can influence speech identification), more dorsal areas appear to be associated with spatial multisensory interactions.

Effects of redundant and nonredundant bimodal sensory stimulation on heart rate in bobwhite quail embryos.

Research with both animal embryos and human infants has provided evidence that information presented redundantly and in temporal synchrony across sensory modalities (intersensory redundancy) can guide selective attention, perceptual learning, and memory during early development. How this facilitation is achieved remains relatively unexamined. This study examined the effects of redundant versus nonredundant bimodal stimulation on a measure of physiological arousal (heart rate) in bobwhite quail embryos. Results show that quail embryos exposed to concurrent but nonredundant auditory and visual stimulation during the late stages of incubation exhibit significantly elevated heart rates following stimulus exposure and during stimulus reexposure when compared to embryos exposed to redundant and synchronous audiovisual stimulation, unimodal auditory stimulation, or no supplemental prenatal sensory stimulation. These findings indicate a functional distinction between redundant and nonredundant bimodal stimulation during early development and suggest that nonredundant bimodal stimulation during the prenatal period can raise arousal levels, thereby potentially interfering with the attentional capacities and perceptual learning of bobwhite quail. In contrast, intersensory redundancy appears to foster arousal levels that facilitate selective attention and perceptual learning during prenatal development.

Interaction of linear vestibular and visual stimulation in the macaque ventral intraparietal area (VIP).

Navigation in space requires the brain to combine information arising from different sensory modalities with the appropriate motor commands. Sensory information about self-motion in particular is provided by the visual and the vestibular system. The macaque ventral intraparietal area (VIP) has recently been shown to be involved in the processing of self-motion information provided by optical flow, to contain multimodal neurons and to receive input from areas involved in the analysis of vestibular information. By studying responses to linear vestibular, visual and bimodal stimulation we aimed at gaining more insight into the mechanisms involved in multimodal integration and self-motion processing. A large proportion of cells (77%) revealed a significant response to passive linear translation of the monkey. Of these cells, 59% encoded information about the direction of self-motion. The phase relationship between vestibular stimulation and neuronal responses covered a broad spectrum, demonstrating the complexity of the spatio-temporal pattern of vestibular information encoded by neurons in area VIP. For 53% of the direction-selective neurons the preferred directions for stimuli of both modalities were the same; they were opposite for the remaining 47% of the neurons. During bimodal stimulation the responses of neurons with opposite direction selectivity in the two modalities were determined either by the visual (53%) or the vestibular (47%) modality. These heterogeneous responses to unimodal and bimodal stimulation might be used to prevent misjudgements about self- and/or object-motion, which could be caused by relying on information of one sensory modality alone.

Wavelet entropy analysis of event-related potentials indicates modality-independent theta dominance

Sensory/cognitive stimulation elicits multiple electroencephalogram (EEG)-oscillations that may be partly or fully overlapping over the time axis. To evaluate co-existent multi-frequency oscillations, EEG responses to unimodal (auditory or visual) and bimodal (combined auditory and visual) stimuli were analyzed by applying a new method called wavelet entropy (WE). The method is based on the wavelet transform (WT) and quantifies entropy of short segments of the event-related brain potentials (ERPs). For each modality, a significant transient decrease of WE emerged in the post-stimulus EEG epoch indicating a highly-ordered state in the ERP. WE minimum was always determined by a prominent dominance of theta (4–8 Hz) ERP components over other frequency bands. Event-related ‘transition to order’ was most pronounced and stable at anterior electrodes, and after bimodal stimulation. Being consistently observed across different modalities, a transient theta-dominated state may reflect a processing stage that is obligatory for stimulus evaluation, during which interfering activations from other frequency networks are minimized.

Sensory system interactions during simultaneous vestibular and visual stimulation in PET.

The patterns of regional cerebral blood flow (rCBF) increases and decreases in PET were compared for unimodal vestibular, unimodal visual, and for simultaneous vestibular and visual stimulation. Thirteen healthy volunteers were exposed to a) caloric vestibular stimulation, b) small-field visual motion stimulation in roll, c) simultaneous caloric vestibular and visual pattern stimulation. Unimodal vestibular stimulation led to activations of vestibular cortex areas, in particular the parieto-insular vestibular cortex (PIVC), and concurrent deactivations of visual cortical areas [Brodmann area (BA) 17-19]. Unimodal visual motion stimulation led to activations of the striate visual cortex and the motion-sensitive area in the middle temporal/middle occipital gyri (BA 19/37) with concurrent deactivations in the PIVC. Simultaneous bimodal stimulation resulted in activations of the cortical representation of both sensory modalities. In the latter condition activations and deactivations were significantly smaller compared to unimodal stimulation. The findings are consistent with the concept of an inhibitory reciprocal vestibulo-visual interaction in all three stimulus conditions.

Intersensory redundancy facilitates prenatal perceptual learning in bobwhite quail (Colinus virginianus) embryos.

Information presented redundantly and in temporal synchrony across sensory modalities (intersensory redundancy) selectively recruits attention and facilitates perceptual learning in human infants. This comparative study examined whether intersensory redundancy also facilitates perceptual learning prenatally. The authors assessed quail (Colinus virginianus) embryos' ability to learn a maternal call when it was (a) unimodal, (b) concurrent but asynchronous with patterned light, or (c) redundant and synchronous with patterned light. Chicks' preference for the familiar over a novel maternal call was assessed 24 hr following hatching. Chicks receiving redundant, synchronous stimulation as embryos learned the call 4 times faster than those who received unimodal exposure. Chicks who received asynchronous bimodal stimulation showed no evidence of learning. These results provide the first evidence that embryos are sensitive to redundant, bimodal information and that it can facilitate learning during the prenatal period.

Wavelet Transform in the analysis of the frequency composition of evoked potentials

This technical paper deals with the application of the Wavelet Transform to the study of evoked potentials. In particular, Wavelet Transform gives an optimal time-dependent frequency decomposition of the evoked responses, something difficult to be achieved with previous methods such as the Fourier Transform. We describe in detail the protocol for implementing the decomposition based on the Wavelet Transform and apply it to two different types of evoked potentials. In the first case we study alpha responses in pattern visual evoked potentials and in the second case, we study gamma responses to bimodal (auditory and visual) stimulation. Although in this study we focus on methodological issues, we briefly discuss physiological implications of the present time–frequency analysis. Furthermore, we show examples of the better performance of the wavelet decomposition in comparison with Fourier-based methods.

Bisensory stimulation increases gamma-responses over multiple cortical regions

In the framework of the discussion about gamma (approx. 40 Hz) oscillations as information carriers in the brain, we investigated the relationship between gamma responses in the EEG and intersensory association. Auditory evoked potentials (AEPs) and visual evoked potentials (VEPs) were compared with bisensory evoked potentials (BEPs; simultaneous auditory and visual stimulation) in 15 subjects. Gamma responses in AEPs, VEPs and BEPs were assessed by means of wavelet decomposition. Overall maximum gamma-components post-stimulus were highest in BEPs ( P<0.01). Bisensory evoked gamma-responses also showed significant central, parietal and occipital amplitude-increases ( P<0.001, P<0.01, P<0.05, respectively; prestimulus interval as baseline). These were of greater magnitude when compared with the unisensory responses. As a correlate of the marked gamma responses to bimodal stimulation we suggest a process of ‘intersensory association’, i.e. one of the steps between sensory transmission and perception. Our data may be interpreted as a further example of function-related gamma responses in the EEG.

The selectively distributed theta system: functions

The present paper provides three interwoven or interrelated approaches: (1) the dependence of frontal theta response from the spontaneous activity will be pointed out. This helps in understanding that ‘frontal theta’ is a major oscillation of the human frontal cortex and has a response-controlling function; (2) it will be shown that complex stimulations such as bimodal stimulation enhances the theta response; and by bringing together the results outlined in a number of previous reviews the so-called ‘selectively distributed theta system of the brain’ is described.

Oscillatory frontal theta responses are increased upon bisensory stimulation

Objectives: To investigate the functional correlation of oscillatory EEG components with the interaction of sensory modalities following simultaneous audio-visual stimulation.Methods: In an experimental study (15 subjects) we compared auditory evoked potentials (AEPs) and visual evoked potentials (VEPs) to bimodal evoked potentials (BEPs; simultaneous auditory and visual stimulation). BEPs were assumed to be brain responses to complex stimuli as a marker for intermodal associative functioning.Results: Frequency domain analysis of these EPs showed marked theta-range components in response to bimodal stimulation. These theta components could not be explained by linear addition of the unimodal responses in the time domain. Considering topography the increased theta-response showed a remarkable frontality in proximity to multimodal association cortices. Referring to methodology we try to demonstrate that, even if various behavioral correlates of brain oscillations exist, common patterns can be extracted by means of a systems-theoretical approach.Conclusions: Serving as an example of functionally relevant brain oscillations, theta responses could be interpreted as an indicator of associative information processing.

Nonlinear system identification and overparameterization effects in multisensory evoked potential studies.

Traditional signal processing techniques have not been suitable in establishing contributions from different sensory paths in multisensory evoked potentials. In this paper, a nonlinear modeling technique is proposed to demonstrate the possible mechanisms of interaction between sensory paths. The nonlinear autoregressive with exogenous inputs (NARX) model is explored to establish a relationship between electrical activities of the brain obtained by unimodal and by bimodal stimulation. The intersensory phenomenon concept is extended using nonlinear system theory and applied to show the possible interactions between the visual and auditory sensory paths. In addition, the paper addresses the compensation phenomenon caused by overparameterization in the NARX algorithm when it is applied to event-related potentials. It is hoped that the nonlinear modeling approach will generate hypotheses about the intersensory interaction phenomenon, improving and advancing its theoretical formulation.

The effect of auditory distractors on saccades toward visual targets

The Findlay-Walker model does not consider saccades generated by auditory targets or nontargets (distractors), or by bimodal stimulation. Empirical results suggest that the effects of auditory stimulation cannot easily be incorporated into the model, neither in the WHEN nor in the WHERE system. A two-stage model by Colonius and Arndt gives a quantitative account of the facilitative effects of auditory distractors on saccadic latencies toward visual targets.

Response amplification in sensory-specific cortices during crossmodal binding

Integrating information across the senses can enhance our ability to detect and classify stimuli in the environment. For example, auditory speech perception is substantially improved when the speaker's face is visible. In an fMRI study designed to investigate the neural mechanisms underlying these crossmodal behavioural gains, bimodal (audio-visual) speech was contrasted against both unimodal (auditory and visual) components. Significant response enhancements in auditory (BA 41/42) and visual (V5) cortices were detected during bimodal stimulation. This effect was found to be specific to semantically congruent crossmodal inputs. These data suggest that the perceptual improvements effected by synthesizing matched multisensory inputs are realised by reciprocal amplification of the signal intensity in participating unimodal cortices.

Combined effects of olfactory and mechanical inputs in antennal lobe neurons of the cockroach

Although it has been known that olfactory and mechanical inputs from the antenna converge in the antennal lobe of the deutocerebrum of the American cockroach, the capacity of antennal lobe neurons to integrate cues from these modalities was never examined. In the present study, neurons responsive to both the odor of lemon oil and to lateral displacement of the antenna were used to compare the effects of unimodal and bimodal stimulation. The combination of olfactory and mechanical stimuli produced increases over unimodal olfactory responses in 61% (30/49) of the neurons. In the remaining neurons the response either decreased (20%; 10/49), or no bimodal interaction was apparent (19%; 9/49). Dye injection (lucifer yellow) following physiological characterization revealed that these bimodal neurons are local neurons or projection neurons. The antennal lobe links the inputs from olfactory and mechanosensory systems and provides a substrate through which olfactory and mechanical stimuli influence one another's effects.

Transcriptional control of sodium transport in tight epithelial by adrenal steroids.

The model for the adrenal steroid action on Na transport in tight epithelia as depicted in Fig. 3A and B dissociates two phases: an early phase during which the pre-existing Na transport machinery is activated and a late phase during which the transport capacity of the machinery is increased. These two sequential phases have been distinguished based on differences in functional aspects of the induced transport, on selective effects of agents interfering with transcriptional regulation and on a correlation of the late response phase with an increase in transport protein synthesis and expression [26, 45, 46, 98, 99, 124]. These observations suggest that a bimodal stimulation of Na transport could involve two different gene networks which are directly (in the physiological meaning) and independently stimulated by the action of the hormone-receptor complex and the following “molecular” cascades (see section Molecular and Physiological Cascades). The relatively clear temporal dissociation of the responses found in experimental situations is probably the consequence of inherent properties of the two networks. Indeed, to generate rapid functional changes, the genes involved in the early response must encode products which have relatively short half-lifes at the mRNA and protein levels. In contrast, the constitutive elements of the Na transport machinery that are increased during the late phase of adrenal steroid action have, as shown for the Na,K-ATPase [82], relatively long half-lifes. Consequently, even though changes in transcription may take place early in the course of the hormonal treatment, they impact on protein synthesis and pools only slowly and after a substantial lag period.

Motor coactivation revealed by response force in divided and focused attention.

Four experiments examined effects of bimodal stimulation on response force (RF) in addition to reaction time (RT). In a divided-attention task (Experiments 1 to 3), subjects were asked for a speeded response to either a visual or an auditory signal. In unimodal signal trials, either a visual or an auditory signal was presented alone, and in redundant-signals trials, both signals were presented simultaneously. The same stimulus arrangement was used in a focused-attention task (Experiment 4), but subjects had to withhold their response when an auditory signal was presented alone. In all experiments, the fastest RTs were attained in redundant-signals trials. In addition, RF was largest in redundant-signals trials, especially in the divided-attention task, suggesting a motor coactivation hypothesis. The results indicate that the type of stimulation influences not only when a response is initiated but also how the response is executed. This finding challenges the view, commonly held in mental chronometry, that late motoric processes remain untouched by experimental manipulations. A detailed analysis of the relationship between RT and RF revealed that these variables are not inherently redundant measures, and, therefore, RF recording may supplement the traditional RT measurement in mental chronometry.

EFFECTS OF OVERT AND COVERT TASKS ON ORIENTING RESPONSE UNDER UNIMODAL AND BIMODAL STIMULATIONS

The present study examined the occurrences of “selective” and “alertive” orienting responses (ORs) in relation to stimulus modality under overt and covert tasks by using electrodermal response (EDR). Two sets of 36 university students received two stimuli (figure and/or tone) during both habituation and test sessions either unimodally (Exp. I) or bimodally (Exp. II). The subjects were assigned to one of three groups during a test session: (1) Key-press which required pressing a key at the offset of the test stimulus, (2) Perceptual-judgment which requested estimating the duration of the test stimulus, or (3) Neutral-instruction which received no task for stimulus presentation. Analysis showed in Exp. I, the first two groups indicated significant increases in EDR magnitudes only in response to the test stimulus, and this EDR increase demonstrated the occurrence of selective OR. In Exp. II, key-press alone showed a significant increase in EDR magnitudes to the nontest stimulus, and this EDR demonstrated the elicitation of alertive OR. The alertive OR emerged clearly when the subject performed an overt task under bimodal stimulation.

Sympathetic skin response: normal results in different experimental conditions

1. (1) The sympathetic skin response (SSR) is a slow wave, generated in deep layers of the skin, resulting from reflex activation of the sudomotor sympathetic efferent fibres. The aim of this study was to define experimental conditions, best stimulation and recording procedures, and the criteria for validation of the responses. 2. (2) Thirty normal subjects (aged 25–56) were tested. The stimulation was an electrical pulse train applied to the median nerve at the wrist, a binaural tone burst, or both simultaneously. Records were made with surface electrodes on hand and foot contralateral to the stimulated median nerve. 3. (3) Response shape was most often biphasic in feet, biphasic or triphasic in hands. SSR amplitude was 3.1 ± 1.8 mV in hands, 1.4 ± 0.8 mV in feet. Normal mean onset latency was 1.5 ± 0.08 sec for hand response, 2.05 ± 0.10 sec for foot response. The mean conduction velovity along peripheral sympathetic nerve fibres was 1.40 ± 0.14 m/sec in lower limbs. 4. (4) Bimodal stimulation (burst + median) provided responses of larger amplitude. The influence of stimulation intensity was also investigated. A decrease in amplitude and lengthening of latencies were observed after 15–20 min of testing. 5. (5) The criteria for validation of responses are discussed. The importance of central processing time in the response delay is pointed out. In good methodological conditions, SSR would appear to be a simple, effective means of assessing sympathetic sudomotor outflow in central and peripheral nervous system disorders.

Further studies on psoriasis-associated HLA-Dw/DR7 using PLT cells primed against a familial psoriasis-linked HLA haplotype.

The products of the HLA-D region and their correlation to psoriasis vulgaris was studied using the primed lymphocyte typing (PLT) assay. In families with one healthy and one psoriatic parent and one psoriatic child primary MLC (mixed lymphocyte culture) stimulation was carried out between responder cells from the healthy parent and stimulator cells from the psoriatic child. In this way 21 PLT reagents directed against putative psoriasis-associated lymphocyte activating determinants were produced. Three reagents that gave clear bimodal stimulation patterns against lymphocytes of 51 psoriasis patients were further tested against 78 controls. Specificity of these reagents was studied using homozygous typing cells (HTC's) as stimulators. Compiled data show that cells from DR7 positive psoriatic patients give higher restimulation of these PLT reagents than do cells from healthy DR7 positive controls. In addition, a higher frequency of psoriasis patients compared to controls gave significant restimulation. Therefore we concluded that these PLT reagents recognized at least partly different DR7 associated determinants in the psoriasis patients and in controls. The reason is either that psoriasis patients carry a different lymphocyte activating DR associated specificity or, alternatively, that restimulation was caused by products of a distinct psoriasis associated locus in linkage disequilibrium with D/DR7 or of a determinant recognized together with D/DR7 as a restriction element. These data further support the notion that psoriasis is a disease with primary HLA associations to both class I and class II MHC genes.