Stimulus Events Research Articles

Two persons with severe post-coma motor impairment and minimally conscious state use assistive technology to access stimulus events and social contact

Arranging and testing environmental/behavioral (i.e., non-medical) intervention programs for persons with severe post-coma motor impairment and minimally conscious state can be very challenging, an...

The Utilisation of Visual Information in the Control of Rapid Interceptive Actions

When intercepting a moving target, accurate timing depends, in part, upon starting to move at the right moment. It is generally believed that this is achieved by triggering motor command generation when a visually perceived quantity such as the target's time-to-arrival reaches a specific criterion value. An experimental method that could be used to determine the moment when this visual event happens was introduced by Whiting and coworkers in the 1970s, and it involves occluding the vision of the target at different times prior to the time of movement onset (MO). This method is limited because the experimenter has no control over MO time. We suggest a method which provides the needed control by having people make interceptive movements of a specific duration. We tested the efficacy of this method in two experiments in which the accuracy of interception was examined under different occlusion conditions. In the first experiment, we examined the effect of changing the timing of an occlusion period (OP) of fixed duration (200 ms). In the second experiment, we varied the duration of the OP (180-430 ms) as well as its timing. The results demonstrated the utility of the proposed method and showed that performance deteriorated only when the participants had their vision occluded from 200 ms prior to MO. The results of Experiment 2 were able to narrow down the critical interval to trigger the interceptive action to within the period from 200 to 150 ms prior to MO, probably closer to 150 ms. In addition, the results showed that the execution of brief interceptive movements (180 ms) was not affected by the range of OPs used in the experiments. This indicates that the whole movement was prepared in advance and triggered by a visual stimulus event that occurred at about 150 ms before onset.

Effects of Prior Information and Reward on Oculomotor and Perceptual Choices

Expectations about the environment influence motor behavior. In simple tasks, for example, prior knowledge about which stimulus event will likely occur or which response will likely be rewarded induces a tendency to take the favored action (i.e., a motor or response bias), especially when sensory information is sparse or ambiguous. Models of choice behavior account for this bias by weighting decision alternatives unequally, either at an early sensory-input stage or at a downstream motor-output stage. These two alternatives can be distinguished empirically; the former predicts an altered percept that correlates with motor bias, the latter predicts no perceptual effect. By varying the prior probability of target or reward location, we induced biased oculomotor responses in a brightness selection task with human subjects. We found that the induced motor bias was correlated with an amplification of both the sensory signals and internal noise underlying brightness perception, without a systematic change in perceived overall brightness. We also found that the magnitude of the sensory amplification was correlated with the amount of noise in the brightness percept, consistent with a multiplicative weighting factor located downstream from the limiting internal sensory noise. Our data demonstrate that prior knowledge (about target location or reward) shapes visual signals for perception and action in parallel but does not improve the quality (i.e., signal-to-noise ratio) of sensory processing.

Somatosensory off-response in humans: An MEG study

We recorded cortical activities in response to the onset and offset of a train of electrical pulses applied to the right hand in eleven healthy volunteers by the use of magnetoencephalograms to clarify temporal and spatial profiles of the somatosensory on- and off-cortical responses. Results showed that a region around the upper bank of the sylvian fissure of both hemispheres responded to the onset and offset of the stimulus, while the activity in the primary somatosensory cortex (SI) of the hemisphere contralateral to the stimulation was clear only for the onset response. The SI activity consisted of two components suggesting that two distinct populations of neurons in SI were involved in processing a train of pulses. The location of the source of activity in the contralateral para-sylvian region (cPara) differed significantly between the on- and off-response, while that of the activity in the ipsilateral para-sylvian region (iPara) did not. The differences in location of the cPara activity might be caused by the overlapping of several cortical activities in response to each stimulus and stimulus event (on and off events), while the iPara activity might reflect purely the event-related response. Moreover, some subjects had clear iPara activity without cPara activity especially in the off-response, suggesting the iPara activity to be independent of the cPara activity. We consider that activities in the parasylvian region are involved in the detection of changes at the body's surface.

Students with multiple disabilities using technology-based programs to choose and access stimulus events alone or with caregiver participation

The first of these two studies extended preliminary evidence on the use of technology-based programs for enabling students with severe and profound multiple disabilities to choose and access environmental stimuli on their own. Each of the three participants had two microswitches linked to specific sets of stimuli through a computer system. The activation of one of the microswitches triggered the computer system to present a sample of one of the stimuli. If the student chose it, the computer system turned it on for a specific time interval. The second study tested a new technology that allowed the students to choose and access the chosen stimuli with the involvement of the caregiver. The two participants had three microswitches linked to a computer system. The participants’ choice of a stimulus alerted the caregiver who then got involved in the stimulation process. The results of both studies showed that the participants learned to activate the basic microswitches consistently, had high percentages of choice for the stimulus samples presented by the computer but with wide differences across stimuli, and largely maintained this performance at a 2-month post-intervention check. These findings were analyzed in terms of the usability of the two types of programs, the role they may play within educational and living contexts, and their innovative technical dimensions.

Attenuation of Neural Responses in Primary Visual Cortex during the Attentional Blink

Information-processing bottlenecks are characteristic of many cognitive and neural systems. One such bottleneck is revealed by tasks in which rapidly successive stimulus events must be reported. Here, observers missed the second of two visual targets if it occurred within 700 ms of the first [an "attentional blink" (AB)], even though this second target could be reported accurately when the first item was ignored. Isolating neural responses to such rapid events has proven difficult because current magnetic resonance imaging methods rely on relatively sluggish changes in the brain's physiological response to sensory inputs. Here, we overcame this limitation by presenting successive visual targets at different spatial locations, thereby exploiting the retinotopic organization of early cortical visual areas to distinguish neural activity associated with successive target events. We show that neural activity in primary visual cortex is significantly modulated during the AB, and that this activity mirrors behavioral measures of target identification accuracy. The findings suggest that the neural signature of perceptual suppression during processing of rapidly successive stimuli is evident at the earliest stages of cortical sensory processing.

Self‐Immolative Comb‐Polymers: Multiple‐Release of Side‐Reporters by a Single Stimulus Event

Self‐Immolative Comb‐Polymers: Multiple‐Release of Side‐Reporters by a Single Stimulus Event

Altered ‘three-flash’ illusion in response to two light pulses in schizophrenia

BackgroundDisorganization is a core dysfunction in schizophrenia. Coherent thought and behavior rely on the interactive neural responses to temporally discrete external events. Previous studies have demonstrated that a single visual stimulus (event) is abnormally affected by another (as in backward masking), but the integration (or ‘synthesis’) of temporally discrete events remains largely unexplored in schizophrenia. We examined the perceived interaction of two elementary visual events in schizophrenia patients, using a psychophysical approach. MethodsTwo brief, spatially-coincident foveal light pulses (5 ms) were presented with different inter-stimulus intervals (ISIs). At ISIs around 100 ms, a substantial proportion of the light pulse pairs was paradoxically perceived as three flashes, a known phenomenon in normal subjects. The subjects reported the number of flashes perceived (‘one’, ‘two’ or ‘three’). ResultsSchizophrenia patients (n=28) reported fewer ‘three flashes’ than normal controls (n=26) at the ISIs where ‘three flash’ reports were greatest in normal subjects (90 to 110 ms). On the other hand, at longer ISIs (130–310 ms) patients reported ‘three flashes’ in more trials than did normal subjects. The perception of three flashes in patients was correlated with certain aspects of clinical status, including the positive and general subscales of the PANSS. DiscussionThe alteration of the ‘three-flash’ illusion in schizophrenia suggests that the synthesis of discrete visual events is temporally ‘dilated’ or distorted, which might contribute to disorganized thought and behavior.

Psychological distress in chronic obstructive pulmonary disease patients

AbstractStress is defined as the exposure of an individual to a threatening stimulus or overwhelming event. Increased rates of psychological distress have been established in patients with chronic diseases compared to healthy individuals. The objective of the present study is to assess the indicators and correlates of psychological distress in chronic obstructive pulmonary disease (COPD) patients.We evaluated the stress exposure (stressful events that COPD patients and control subjects had been exposed) by a life events checklist and psychological distress by General Health Questionnaire in 74 COPD patients and 30 control subjects. Serum adrenocorticotropic hormone (ACTH) and cortisol levels were measured as biochemical indicators of stress.Distress score was higher in COPD group compared to age‐matched controls, although the stress exposure score were not statistically different; indicating that COPD itself is a source of distress. 92% of COPD patients and 87% of control subjects had varying degrees of distress. Severe distress was more frequent in COPD group. Distress score was further increased in patients with severe COPD and severe hypoxemia.There was no significant difference in serum ACTH and cortisol levels of COPD patients and control subjects and distress scores were not correlated to serum ACTH and cortisol levels. However, serum cortisol was higher in patients with severe hypoxemia.These findings support the importance of screening for psychological distress symptoms in COPD outpatients. Since high degree of distress contributes to impaired quality of life and added morbidity, patients with COPD need a comprehensive care including a psychological evaluation. Copyright © 2008 John Wiley & Sons, Ltd.

MEG event-related desynchronization and synchronization deficits during basic somatosensory processing in individuals with ADHD

BackgroundAttention-Deficit/Hyperactivity Disorder (ADHD) is a prevalent, complex disorder which is characterized by symptoms of inattention, hyperactivity, and impulsivity. Convergent evidence from neurobiological studies of ADHD identifies dysfunction in fronto-striatal-cerebellar circuitry as the source of behavioural deficits. Recent studies have shown that regions governing basic sensory processing, such as the somatosensory cortex, show abnormalities in those with ADHD suggesting that these processes may also be compromised.MethodsWe used event-related magnetoencephalography (MEG) to examine patterns of cortical rhythms in the primary (SI) and secondary (SII) somatosensory cortices in response to median nerve stimulation, in 9 adults with ADHD and 10 healthy controls. Stimuli were brief (0.2 ms) non-painful electrical pulses presented to the median nerve in two counterbalanced conditions: unpredictable and predictable stimulus presentation. We measured changes in strength, synchronicity, and frequency of cortical rhythms.ResultsHealthy comparison group showed strong event-related desynchrony and synchrony in SI and SII. By contrast, those with ADHD showed significantly weaker event-related desynchrony and event-related synchrony in the alpha (8–12 Hz) and beta (15–30 Hz) bands, respectively. This was most striking during random presentation of median nerve stimulation. Adults with ADHD showed significantly shorter duration of beta rebound in both SI and SII except for when the onset of the stimulus event could be predicted. In this case, the rhythmicity of SI (but not SII) in the ADHD group did not differ from that of controls.ConclusionOur findings suggest that somatosensory processing is altered in individuals with ADHD. MEG constitutes a promising approach to profiling patterns of neural activity during the processing of sensory input (e.g., detection of a tactile stimulus, stimulus predictability) and facilitating our understanding of how basic sensory processing may underlie and/or be influenced by more complex neural networks involved in higher order processing.

The azaquinone-methide elimination: comparison study of 1,6- and 1,4-eliminations under physiological conditions

The azaquinone-methide elimination is a powerful and efficient reaction useful for disassembly of spacers in prodrug systems. We and others have used the spacer-technique to develop dendritic and polymeric self-immolative molecular systems that can disassemble through a domino-like mechanism upon a stimulus event. In this report, we study the disassembly of a system that can disintegrate through para- and ortho-azaquinone-methide eliminations. The disassembly was evaluated with molecules that undergo single 1,6- or 1,4-elimination and with molecules that undergo double 1,6- and 1,4-elimination. The 1,6-elimination was slightly faster than the 1,4-elimination under physiological conditions. This study sheds light on the disassembly-behavior of prodrug systems.

Antiphonal exchanges in African elephants (Loxodonta africana): collective response to a shared stimulus, social facilitation, or true communicative event?

AbstractFemale African elephants are thought to exchange 'rumble' vocalizations, but such temporally associated calls may not constitute communicative events. Affiliated females are more likely to engage in antiphonal calling, but affiliation is defined according to time spent in proximity. Affiliated partners may vocalize in sequence simply because their proximity causes them to collectively respond to shared external stimuli or due to a social facilitation effect. We used bi-variate and partial correlation analyses to test for the independent effects of the strength of the social relationship and distance between vocal partners on the likelihood of a vocal response. Female African elephants at Disney's Animal Kingdom were video-taped and outfitted with audio-recording collars that allowed for the individual identification of low-frequency rumbles. Affiliation had a strong influence on response likelihood, even after controlling for the effects of the distance between vocalizing partners. Further, the distance between vocalizing partners did not correlate with response likelihood, and factoring out the effects of affiliation did not significantly alter this result. These results suggest that rumble exchanges are communicative events that reflect social bonds, not simply artifacts of increased proximity and, therefore, provide support for functional hypotheses concerning rumble exchanges in wild African elephants.

A Salience Theory of Learning and Behavior: With Perspectives on Neurobiology and Cognition

Traditional behaviorists have described behaviors fundamentally as responses to stimuli or, perhaps more liberally, as behaviors under the control of discriminative stimuli or contexts. They have held responses or behaviors to be established, strengthened, sustained, and inhibited or extinguished by contingent events: notably reinforcers, punishers, or the absence of either. In addition, they believed reinforcement acts on the response, the behavior, not on the organism. Here, and in support of Hebb’s view, we advance a contrarian view. A key principle of our framework is that species’ brains are uniquely designed to perceive and to relate stimulus events that are contiguous, salient, and relevant to adaptation. In accordance with what we here view as the constructive biases of species’ brains, stimuli are differentially organized into amalgams that reflect an exchange of salience and response-eliciting properties of component units, which are then integrated to form a basis of knowledge about the organism and its ecological niche. One can then base adaptation on overarching principles and rules, not just on simple associations. Species may create emergent behaviors with no history of specific training, and even new capacities, to service adaptation to both familiar and novel challenges.

Improved flash evoked response from fetal MEG

We have evaluated a newly implemented optical stimulator in a fetal MEG system for effectiveness of eliciting fetal flash evoked response using 29 normal, low-risk fetuses. MEG recordings were performed with a 151 channel array conforming to the maternal abdomen. Interference from maternal and fetal heart was attenuated by orthogonal projection and stimulus events were averaged to improve SNR after rejection of data segments with fetal motion. The responses identified by visual examination of the averaged time courses were subjected to validation by a significance measure based on a bootstrap confidence interval computation. The second generation stimulator increased comfort and ease of placement between the maternal abdomen and sensor array while delivering greater optical power to the fetus. After discarding 2 measurements for excessive artifact, averaged evoked responses with good baseline above background noise levels were observed in 24 recordings resulting in a detection rate of 89%; 26% greater than previously reported by our group using a first generation stimulator. Use of the new fetal visual stimulation delivery system resulted in an increased detection rate of fetal flash evoked response and the bootstrap significance measure provided some validation of results.

Saccade landing point selection and the competition account of pro‐ and antisaccade generation: The involvement of visual attention – A review

This paper presents a review and summary of experimental findings on the role of attention in the preparation of saccadic eye movements. The focus is on experiments where performance of prosaccades (saccades towards a suddenly appearing item) and antisaccades (saccades of equal amplitude in the direction opposite to where the target moved) is compared. Evidence suggests that these two opposite responses to the same stimulus event entail competition between neural pathways that generate reflexive movements to the target and neural mechanisms involved in inhibiting the reflex and generating a voluntary gaze shift in the opposite direction to the target appearance. Evidence for such a competition account is discussed in light of a large amount of experimental findings and the overall picture clearly indicates that this competition account has great explanatory power when data on saccadic reaction times and error rates are compared for the two types of saccade. The role of attention is also discussed in particular in light of the finding that the withdrawal of attention by a secondary task 200 to 500 ms before the saccade target appears, leads to speeded antisaccades (without a similar increase in error rates), showing that the results do not simply reflect a speed-accuracy trade-off. This result indicates that the tendency for "reflexive" prosaccades is diminished when attention is engaged in a different task. Furthermore, experiments are discussed that show that as the tendency for a reflexive prosaccade is weakened, antisaccades are speeded up, further supporting the competition account of pro- and antisaccade generation. In the light of evidence from neurophysiology of monkeys and humans, a tentative model of pro- and antisaccade generation is proposed.

Retinal Ganglion Cells Can Rapidly Change Polarity from Off to On

Retinal ganglion cells are commonly classified as On-center or Off-center depending on whether they are excited predominantly by brightening or dimming within the receptive field. Here we report that many ganglion cells in the salamander retina can switch from one response type to the other, depending on stimulus events far from the receptive field. Specifically, a shift of the peripheral image—as produced by a rapid eye movement—causes a brief transition in visual sensitivity from Off-type to On-type for approximately 100 ms. We show that these ganglion cells receive inputs from both On and Off bipolar cells, and the Off inputs are normally dominant. The peripheral shift strongly modulates the strength of these two inputs in opposite directions, facilitating the On pathway and suppressing the Off pathway. Furthermore, we identify certain wide-field amacrine cells that contribute to this modulation. Depolarizing such an amacrine cell affects nearby ganglion cells in the same way as the peripheral image shift, facilitating the On inputs and suppressing the Off inputs. This study illustrates how inhibitory interneurons can rapidly gate the flow of information within a circuit, dramatically altering the behavior of the principal neurons in the course of a computation.

Evaluation of Cortical Connectivity During Real and Imagined Rhythmic Finger Tapping

Accumulating evidence suggests the existence of a shared neural substrate between imagined and executed movements. However, a better understanding of the mechanisms involved in the motor execution and motor imagery requires knowledge of the way the co-activated brain regions interact to each other during the particular (real or imagined) motor task. Within this general framework, the aim of the present study is to investigate the cortical activation and connectivity sub-serving real and imaginary rhythmic finger tapping, from the analysis of multi-channel electroencephalogram (EEG) scalp recordings. A sequence of 250 auditory pacing stimuli has been used for both the real and imagined right finger tapping task, with a constant inter-stimulus interval of 1.5 s length. During the motor execution, healthy subjects were asked to tap in synchrony with the regular sequence of stimulus events, whereas in the imagery condition subjects imagined themselves tapping in time with the auditory cue. To improve the spatial resolution of the scalp fields and suppress unwanted interferences, the EEG data have been spatially filtered. Further, event related synchronization and desynchronization phenomena and phase synchronization analysis have been employed for the study of functionally active brain areas and their connectivity during real and imagery finger tapping. Our results show a fronto-parietal co-activation during both real and imagined movements and similar connectivity patterns among contralateral brain areas. The results support the hypothesis that functional connectivity over the contralateral hemisphere during finger tapping is preserved in imagery. The approach and results can be regarded as indicative evidences of a new strategy for recognizing imagined movements in EEG-based brain computer interface research.

The distributed auditory cortex

A synthesis of cat auditory cortex (AC) organization is presented in which the extrinsic and intrinsic connections interact to derive a unified profile of the auditory stream and use it to direct and modify cortical and subcortical information flow. Thus, the thalamocortical input provides essential sensory information about peripheral stimulus events, which AC redirects locally for feature extraction, and then conveys to parallel auditory, multisensory, premotor, limbic, and cognitive centers for further analysis. The corticofugal output influences areas as remote as the pons and the cochlear nucleus, structures whose effects upon AC are entirely indirect, and it has diverse roles in the transmission of information through the medial geniculate body and inferior colliculus. The distributed AC is thus construed as a functional network in which the auditory percept is assembled for subsequent redistribution in sensory, premotor, and cognitive streams contingent on the derived interpretation of the acoustic events. The confluence of auditory and multisensory streams likely precedes cognitive processing of sound. The distributed AC constitutes the largest and arguably the most complete representation of the auditory world. Many facets of this scheme may apply in rodent and primate AC as well. We propose that the distributed auditory cortex contributes to local processing regimes in regions as disparate as the frontal pole and the cochlear nucleus to construct the acoustic percept.

Invited Commentary on Animal Models in Psychiatry: Animal Models of Non-conventional Human Behavior

Conventional behavior, of which linguistic behavior is the principal variety, is identified as responses having formal properties that are not determined by the natural properties of stimulus objects, but instead by properties attributed to those objects under the auspices of particular groups. Given the ubiquity of this type of behavior in the repertoires of human beings and its complete absence in those of non-humans, the argument is made that animal models of human disorders, in which disturbances of conventional behaviors constitute defining features, are not sufficiently analogous to these conditions in humans to be pursued with good result. Because conventional behavior of the linguistic type is ubiquitous in the repertoires of normally developed human adults, it is suggested that the behavior of pre-verbal infants and/or non-verbal persons is preferable to that of adults as the phenomenal source for the construction of animal models of human psychological events. The observation and measurement of psychological events is held to be complicated by a number of their characteristics, including their complexity by virtue of whole organism participation, their essential complementarily with stimulus events, and the corrigibility of both form and function over their repeated occurrences, among others. The implications of these features for modeling enterprises are discussed.

A Moment to Reflect upon Perceptual Synchrony

How does neuronal activity bring about the interpretation of visual space in terms of objects or complex perceptual events? If they group, simple visual features can bring about the integration of spikes from neurons responding to different features to within a few milliseconds. Considered as a potential solution to the "binding problem," it is suggested that neuronal synchronization is the glue for binding together different features of the same object. This idea receives some support from correlated- and periodic-stimulus motion paradigms, both of which suggest that the segregation of a figure from ground is a direct result of the temporal correlation of visual signals. One could say that perception of a highly correlated visual structure permits space to be bound in time. However, on closer analysis, the concept of perceptual synchrony is insufficient to explain the conditions under which events will be seen as simultaneous. Instead, the grouping effects ascribed to perceptual synchrony are better explained in terms of the intervals of time over which stimulus events integrate and seem to occur simultaneously. This point is supported by the equivalence of some of these measures with well-established estimates of the perceptual moment. However, it is time in extension and not the instantaneous that may best describe how seemingly simultaneous features group. This means that studies of perceptual synchrony are insufficient to address the binding problem.