Presentation Of Visual Stimuli Research Articles

Sustained versus transient brain responses in schizophrenia: the role of intrinsic neural activity

Schizophrenia patients (SZ) show early visual processing deficits in many, but not all, tasks. These deficits may be associated with dysregulation of intrinsic oscillatory activity that compromises signal-to-noise in the SZ brain. This question was studied using visual steady-state stimulation and post-steady-state presentation of transient visual stimuli. SZ had higher intrinsic oscillatory activity at the steady-state stimulation frequency (12.5Hz) and at the 6.25Hz subharmonic, showed a significant decrease in visual steady-state magnitude over 2s of stimulation, and were unable to promptly terminate the steady-state response following stimulation offset. If adjustment for levels of intrinsic brain activity were made, however, it would have appeared that SZ had activity of similar magnitude as healthy subjects following steady-state stimulus termination, indicating that such adjustments could substantially alter theoretical interpretations. Visual evoked potential abnormalities (N1/P2 amplitudes) present among SZ at the initiation of steady-state stimulation were less apparent in the 750ms immediately following steady-state stimulation offset. Higher intrinsic oscillatory brain activity may be a fundamental characteristic of SZ that merits further evaluation for understanding this disorder's neuropathological correlates and associated symptomatology.

Visual awareness suppression by pre-stimulus brain stimulation; a neural effect

Transcranial magnetic stimulation (TMS) has established the functional relevance of early visual cortex (EVC) for visual awareness with great temporal specificity non-invasively in conscious human volunteers. Many studies have found a suppressive effect when TMS was applied over EVC 80-100 ms after the onset of the visual stimulus (post-stimulus TMS time window). Yet, few studies found task performance to also suffer when TMS was applied even before visual stimulus presentation (pre-stimulus TMS time window). This pre-stimulus TMS effect, however, remains controversially debated and its origin had mainly been ascribed to TMS-induced eye-blinking artifacts. Here, we applied chronometric TMS over EVC during the execution of a visual discrimination task, covering an exhaustive range of visual stimulus-locked TMS time windows ranging from -80 pre-stimulus to 300 ms post-stimulus onset. Electrooculographical (EoG) recordings, sham TMS stimulation, and vertex TMS stimulation controlled for different types of non-neural TMS effects. Our findings clearly reveal TMS-induced masking effects for both pre- and post-stimulus time windows, and for both objective visual discrimination performance and subjective visibility. Importantly, all effects proved to be still present after post hoc removal of eye blink trials, suggesting a neural origin for the pre-stimulus TMS suppression effect on visual awareness. We speculate based on our data that TMS exerts its pre-stimulus effect via generation of a neural state which interacts with subsequent visual input.

Effects of sleep deprivation on cortical activation during directed attention in the absence and presence of visual stimuli

Sleep deprivation (SD) can give rise to faltering attention but the mechanics underlying this remain uncertain. Using a covert attention task that required attention to a peripheral target location, we compared the effects of attention and SD on baseline activity prior to visual stimulation as well as on stimulus-evoked activity. Volunteers were studied after a night of normal sleep (RW) and a night of SD. Baseline signal elevations evoked by preparatory attention in the absence of visual stimulation were attenuated within rFEF, rIPS (sparing SEF) and all retinotopically mapped visual areas during SD, indicative of impaired endogenous attention. In response to visual stimuli, attention modulated activation in higher cortical areas and extrastriate cortex (hV4, ventral occipital areas) after RW. SD attenuated rFEF, rIPS, V3a and VO stimulus-evoked activation regardless of whether stimuli were attended. Notably, the modulation of stimulus-evoked activation by attention was not affected by SD unlike for the preparatory period, suggesting a reduced number, but still functional circuits during SD. Deficits in endogenous attention in SD dominate in the preparatory period, whereas changes in stimulus-related activation arise from an interaction between compromised fronto-parietal top-down control of attention and reduced sensitivity of extrastriate visual cortex to top-down or bottom-up inputs.

MSTd Neurons Encode Nonlinear Combinations of Retinal and Extra-retinal Signals

AbstractNeuronal activity in the dorsal Medial Superior Temporal area (MSTd) is assumed to depend on both retinal and extra-retinal input. Most of the neurons show activity when presented with a moving large-field visual stimulus. In addition, many MSTd neurons are activated during smooth pursuit eye movements even in the absence of retinal input. However, the interaction between the retinal and extra-retinal input is not yet fully understood.Here we present novel insights regarding the tuning of MSTd neurons for combinations of different input variables using an information-theoretic approach. Neuronal tuning functions can be expressed by the conditional probability of observing a spike given any combination of input variables. However, accurately determining such probabilistic tuning functions from experimental data poses several challenges such as determining the neuronal latencies and finding the combination of input variables which is most related to neuronal activity. Our approach solves these issues by maximizing the mutual information between the probability distributions of spike occurrence and input variables.We analyzed the dependence of MSTd neuronal activity in monkeys on various retinal and extra-retinal signals during presentation of a large-field visual stimulus moving randomly with quasi equally distributed frequencies (white noise). Across the population, neuronal activity depended on different combinations of retinal and extra-retinal input. The interrelation between the input variables exhibited in many cases strong non-linear characteristics. These findings support the hypothesis that MSTd uses a basis function representation for encoding various retinal and extra-retinal signals.

Lesion of Primary Visual Cortex in Monkey Impairs the Inhibitory but Not the Facilitatory Cueing Effect on Saccade

Prior visual stimulus presentation induces immediate facilitation and subsequent inhibition of orienting to an ensuing target at the same location. Recent studies revealed that the superior colliculus (SC) is involved in these facilitatory and inhibitory cueing effects on saccade; however, as the SC receives inputs both directly from the retina (retino-tectal pathway) and indirectly from visual cortices (geniculostriate pathway), it is unclear which visual pathway contributes to the effects. We investigated this issue using monkeys with lesions in the primary visual cortex (V1), thus depriving the SC of the geniculostriate pathway and leaving the retino-tectal pathway intact. We found that the inhibitory cueing effect was selectively impaired and the facilitatory cueing effect was spared after V1 lesions. The results suggest that the geniculostriate and the retino-tectal pathways are differentially involved in the generation of cueing effects on saccade: The former is critically involved in the inhibitory effect whereas the latter alone can induce the facilitatory effect. The results provide the first direct evidence for the involvement of the geniculostriate pathway in the inhibitory cueing effect and further imply that the more recent evolution of the geniculostriate pathway in higher mammals improves the efficiency of visual search by inhibiting orienting to a previously attended location.

Overcoming Memory Limitations in Rule Learning

Adults, infants, and other species are able to learn and generalize abstract patterns from sequentially presented stimuli. Rule learning of this type may be involved in children's acquisition of linguistic structure, but the nature of the mechanisms underlying these abilities is unknown. While inferences regarding the capabilities of these mechanisms are commonly made based on the pattern of successes and failures in simple artificial-language rule-learning tasks, failures may be driven by memory limitations rather than intrinsic limitations on the kinds of computations that learners can perform. Here we show that alleviating memory constraints on adult learners through concurrent visual presentation of stimuli allowed them to succeed in learning regularities in three difficult artificial rule-learning experiments where participants had previously failed to learn via sequential auditory presentation. These results suggest that memory constraints, rather than intrinsic limitations on learning, may be a parsimonious explanation for many previously reported failures. We argue that future work should attempt to characterize the role of memory constraints in natural and artificial language learning.

EEG alpha activity in the human brain during perception of an illusory kanizsa square

We investigated the temporospatial dynamics of the power of the phase-linked component and the total power of EEG alpha oscillations on presentation of an illusory outline (Kanizsa square) and a control nonillusory image to 16 healthy adult subjects. Alpha oscillations were identified using wavelets; statistical assessments of the dynamics of alpha power were studied by analysis of variance, along with a new nonparametric multifactorial analysis method. Presentation of visual stimuli was found to be accompanied by early increases in the total power of alpha oscillations, which were more marked on perception of the illusory outline as compared with the control stimulus (the “illusion effect”). This early short phase of the alpha response arose mainly because of the phase-linked component, and was followed by a longer-lasting phase of depression of the total power of alpha oscillations (“alpha rhythm blockade”), which was nonspecific in relation to the type of stimulus. Both phases of the alpha response were most marked in the parietal-temporal-occipital areas of the right hemisphere. We propose that the first increase in alpha oscillations reflects modulation of the activity of neuron ensembles involved in processing the overall patterns, while alpha rhythm blockade is associated with orientation processes.

Electroencephalographic Brain Dynamics of Memory Encoding in Emotionally Arousing Context

Emotional content/context enhances declarative memory through modulation of encoding and retrieval mechanisms. At encoding, neurophysiological data have consistently demonstrated the subsequent memory effect in theta and gamma oscillations. Yet, the existing studies were focused on the emotional content effect and let the emotional context effect unexplored. We hypothesized that theta and gamma oscillations show higher evoked/induced activity during the encoding of visual stimuli when delivered in an emotionally arousing context. Twenty-five healthy volunteers underwent evoked potentials (EP) recordings using a 21 scalp electrodes montage. They attended to an audiovisual test of emotional declarative memory being randomly assigned to either emotionally arousing or neutral context. Visual stimulus presentation was used as the time-locking event. Grand-averages of the EP and evoked spectral perturbations were calculated for each volunteer. EP showed a higher negative deflection from 80 to 140 ms for the emotional condition. Such effect was observed over central, frontal and prefrontal locations bilaterally. Evoked theta power was higher in left parietal, central, frontal, and prefrontal electrodes from −50 to 300 ms in the emotional condition. Evoked gamma power was higher in the emotional condition with a spatial distribution that overlapped at some points with the theta topography. The early theta power increase could be related to expectancy induced by auditory information processing that facilitates visual encoding in emotional contexts. Together, our results suggest that declarative memory enhancement for both emotional content and emotional context are supported by similar neural mechanisms at encoding, and offer new evidence about the brain processing of relevant environmental stimuli.

Probing of Brain States in Real-Time: Introducing the ConSole Environment

Recent years have seen huge advancements in the methods available and used in neuroscience employing EEG or MEG. However, the standard approach is to average a large number of trials for experimentally defined conditions in order to reduce intertrial-variability, i.e., treating it as a source of “noise.” Yet it is now more and more accepted that trial-to-trial fluctuations bear functional significance, reflecting fluctuations of “brain states” that predispose perception and action. Such effects are often revealed in a pre-stimulus period, when comparing response variability to an invariant stimulus. However such offline analyses are disadvantageous as they are correlational by drawing conclusions in a post hoc-manner and stimulus presentation is random with respect to the feature of interest. A more direct test is to trigger stimulus presentation when the relevant feature is present. The current paper introduces Constance System for Online EEG (ConSole), a software package capable of analyzing ongoing EEG/MEG in real-time and presenting auditory and visual stimuli via internal routines. Stimulation via external devices (e.g., transcranial magnetic stimulation) or third-party software (e.g., PsyScope X) is possible by sending TTL-triggers. With ConSole it is thus possible to target the stimulation at specific brain states. In contrast to many available applications, ConSole is open-source. Its modular design enhances the power of the software as it can be easily adapted to new challenges and writing new experiments is an easy task. ConSole is already pre-equipped with modules performing standard signal processing steps. The software is also independent from the EEG/MEG system, as long as a driver can be written (currently two EEG systems are supported). Besides a general introduction, we present benchmark data regarding performance and validity of the calculations used, as well as three example applications of ConSole in different settings. ConSole can be downloaded at: http://console-kn.sf.net.

Fast dopamine release events in the nucleus accumbens of early adolescent rats

Subsecond fluctuations in dopamine (dopamine transients) in the nucleus accumbens are often time-locked to rewards and cues and provide an important learning signal during reward processing. As the mesolimbic dopamine system undergoes dynamic changes during adolescence in the rat, it is possible that dopamine transients encode reward and stimulus presentations differently in adolescents. However, to date no measurements of dopamine transients in awake adolescents have been made. Thus, we used fast scan cyclic voltammetry to measure dopamine transients in the nucleus accumbens core of male rats (29–30 days of age) at baseline and with the presentation of various stimuli that have been shown to trigger dopamine release in adult rats. We found that dopamine transients were detectable in adolescent rats and occurred at a baseline rate similar to adult rats (71–72 days of age). However, unlike adults, adolescent rats did not reliably exhibit dopamine transients at the unexpected presentation of visual, audible and odorous stimuli. In contrast, brief interaction with another rat increased dopamine transients in both adolescent and adult rats. While this effect habituated in adults at a second interaction, it persisted in the adolescents. These data are the first demonstration of dopamine transients in adolescent rats and reveal an important divergence from adults in the occurrence of these transients that may result in differential learning about rewards.

Visual Biasing of Auditory Localization in Azimuth and Depth

Correctly integrating sensory information across different modalities is a vital task, yet there are illusions which cause the incorrect localization of multisensory stimuli. A common example of these phenomena is the "ventriloquism effect". In this illusion, the localization of auditory signals is biased by the presence of visual stimuli. For instance, when a light and sound are simultaneously presented, observers may erroneously locate the sound closer to the light than its actual position. While this phenomenon has been studied extensively in azimuth at a single depth, little is known about the interactions of stimuli at different depth planes. In the current experiment, virtual acoustics and stereo-image displays were used to test the integration of visual and auditory signals across azimuth and depth. The results suggest that greater variability in the localization of sounds in depth may lead to a greater bias from visual stimuli in depth than in azimuth. These results offer interesting implications for understanding multisensory integration.

Wavelet basis functions in biomedical signal processing

During the last two decades, wavelet transform has become a common signal processing technique in various areas. Selection of the most similar mother wavelet function has been a challenge for the application of wavelet transform in signal processing. This paper introduces Daubechies 44 (db44) as the most similar mother wavelet function across a variety of biological signals. Three-hundred and twenty four potential mother wavelet functions were selected and investigated in the search for the most similar function. The algorithms were validated by three categories of biological signals: forearm electromyographic (EMG), electroencephalographic (EEG), and vaginal pulse amplitude (VPA). Surface and intramuscular EMG signals were collected from multiple locations on the upper forearm of subjects during ten hand motions. EEG was recorded from three monopolar Ag–AgCl electrodes (Pz, POz, and Oz) during visual stimulus presentation. VPA, a useful source for female sexuality research, were recorded during a study of alcohol and stimuli on sexual behaviors. In this research, after extensive studies on mother wavelet functions, results show that db44 has the most similarity across these classes of biosignals.

Applying Skinner's Analysis of Verbal Behavior to Persons With Dementia

Skinner's 1957 analysis of verbal behavior has demonstrated a fair amount of utility to teach language to children with autism and other various disorders. However, the learning of language can be forgotten, as is the case for many elderly suffering from dementia or other degenerative diseases. It appears possible that Skinner's operants may facilitate not only acquisition of language but also the ability to recall items or objects that may have appeared to be “forgotten.” The present study examined the utility of having a series of adults in long-term care emit tacts, echoics, or intraverbals upon presentation of various visual stimuli. Compared to a no-verbal response condition, it appears that the incorporation of Skinner's verbal operants can in fact improve recall for this population. Implications for the retraining of lost language are presented.

Affect 4.0

We describe Affect 4.0, a user-friendly software package for implementing psychological and psychophysiological experiments. Affect 4.0 can be used to present visual, acoustic, and/or tactile stimuli in highly complex (i.e., semirandomized and response-contingent) sequences. Affect 4.0 is capable of registering response latencies and analog behavioral input with millisecond accuracy. Affect 4.0 is available free of charge.

Neuronal Responses during and after the Presentation of Static Visual Stimuli in Macaque Primary Visual Cortex

Viewing static visual scenes for several seconds or longer can induce a wide variety of striking percepts, including negative afterimages, fading, and motion aftereffects. To characterize the neuronal bases of such phenomena and elucidate functional circuitry in the visual system, we recorded responses of neurons in primary visual cortex (V1) of anesthetized macaques during and after the presentation of prolonged static visual stimuli. We found that 72% of cells generated significant after-responses (ARs) that outlasted classical off-transients after the cessation of stimuli, and AR amplitude grew with stimulus duration. After the longest stimuli tested (32 s), the amplitude and the time course of the AR were on average comparable to, and correlated with, those of the maintained response evoked while stimuli were present. These observations generally held regardless of cell class: simple, complex, direction selective (DS) or non-DS. The average decay time constant of the AR for orientation-tuned cells was 0.65 s. This is strikingly shorter than time constants observed in the lateral geniculate nucleus, which were on the order of tens of seconds. Cells in V1 that lacked orientation tuning displayed an intermediate time course, with a mean time constant of 4.3 s. These results are consistent with a multistage model in which cells at successive stages adapt to their inputs with progressively shorter time constants. Our findings suggest that the perceptual phenomena of fading and afterimages are shaped by both cortical and subcortical dynamics and provide a physiological framework for the interpretation of recent and long-standing psychophysical observations.

Interruption of visually perceived forward motion in depth evokes a cortical activation shift from spatial to intentional motor regions

Forward locomotion generates a radially expanding flow of visual motion which supports goal-directed walking. In stationary mode, wide-field visual presentation of optic flow stimuli evokes the illusion of forward self-motion. These effects illustrate an intimate relation between visual and motor processing. In the present fMRI study, we applied optic flow to identify distinct interfaces between circuitries implicated in vision and movement. The dorsal premotor cortex (PMd) was expected to contribute to wide-field forward motion flow (FFw), reflecting a pathway for externally triggered motor control. Medial prefrontal activation was expected to follow interrupted optic flow urging internally generated action. Data of 15 healthy subjects were analyzed with Statistical Parametric Mapping and confirmed this hypothesis. Right PMd activation was seen in FFw, together with activations of posterior parietal cortex, ventral V5, and the right fusiform gyrus. Conjunction analysis of the transition from wide to narrow forward flow and reversed wide-field flow revealed selective dorsal medial prefrontal activation. These findings point at equivalent visuomotor transformations in locomotion and goal-directed hand movement, in which parietal–premotor circuitry is crucially implicated. Possible implications of an activation shift from spatial to intentional motor regions for understanding freezing of gait in Parkinson's disease are discussed: impaired medial prefrontal function in Parkinson's disease may reflect an insufficient internal motor drive when visual support from optic flow is reduced at the entrance of a narrow corridor.

Achieving precise display timing in visual neuroscience experiments

In experimental visual neuroscience brief presentations of visual stimuli are often required. Accurate knowledge of the durations of visual stimuli and their signal shapes is important in psychophysical experiments with humans and in neuronal recordings with animals. In this study we measure and analyze the changes in luminance of visual stimuli on standard computer monitors. Signal properties of the two most frequently used monitor technologies, cathode ray tube (CRT) and liquid crystal display (LCD) monitors, are compared, and the effects of the signal shapes on the stated durations of visual stimuli are analyzed. The fundamental differences between CRT and LCD signals require different methods for the specification of durations, especially for brief stimulus presentations. In addition, stimulus durations on LCD monitors vary over different monitor models and are not even homogeneous with respect to different luminance levels on a single monitor. The use of LCD technology for brief stimulus presentation requires extensive display measurements prior to the experiment.

Age-related differences on cognitive overload in an audio-visual memory task

The present study aimed to provide evidence outlining whether the type of stimuli used in teaching would provoke differing levels of recall across three different academic age groups. One hundred and twenty-one participants, aged 11–25 years, were given a language-based memory task in the form of a wordlist consisting of 15 concrete and 15 abstract words, presented either visually, acoustically, or a combination of both audio and visual presentation. The study found that the presence of cognitive overload was greater in the older academic age participants than in the younger groups and that as academic experience increased, the visual presentation of the target stimuli produced greater levels of recall than was the case with acoustic and audio-visual presentation. Overall the findings indicate that cognitive overload increases with age, as the younger-age groups were found to have significantly higher levels of word recall in the audio-visual condition than the older groups.

I know the pain you feel—how the human brain's default mode predicts our resonance to another's suffering

Introspective and self-referential in nature, the human brain's default mode network (DMN) is presumed to influence our behavior in response to the environment in predictive manner [Raichle ME, Gusnard DA (2005) J Comp Neurol 493:167–176; Bar M (2009) Philos Trans R Soc Lond B Biol Sci 364:1235–1243]. In the current study, we hypothesize that the strength of DMN-connectivity contributes to distinct introspective psychological processes in every-day social life such as the intuitive understanding of other people through inner representation of their affective states −e. g. his or her pain. 19 healthy individuals underwent functional MRI scanning, which consisted of a resting-state-scan followed by the presentation of visual stimuli depicting human limbs in painful and non-painful situations. After scanning, participants were asked to evaluate the stimuli in terms of pain intensity perceived from the first person perspective. Independent component analysis (ICA) demonstrated that higher integration of the left medial orbitofrontal cortex (BA 32) into the anterior default mode network (aDMN) was associated with higher post-scan pain ratings. Furthermore, the exposition to the “Pain”-pictures led to relative increases of aDMN-activity compared to “No Pain”-stimuli which were also correlated with the subjective pain intensity. The behaviorally predictive functional architecture during a task-free period supports the notion that the DMN serves as a “memory of the future” [Ingvar DH (1985) Hum Neurobiol 4:127–136] in terms of a neuronal cache, storing “a priori scripts,” which are recalled to deal efficiently with upcoming environmental events. In addition, our results suggest that an individual predisposition to identify oneself with another's pain influences the automatic response of the DMN during the observation of painful situations.

직물의 마찰음에 대한 감성 평가 및 예측 시스템 개발

Research has been conducted to examine the effects of mechanical and sound characteristics of fabrics on affective quality. The present study developed the Affective Quality Evaluation and Estimation System for Textiles (AQEEST) with distinguished features that can be effectively used in the affective research of fabric frictional sound. The AQEEST consists of three subsystems (affective quality evaluation, affective quality estimation, and audible distance estimation subsystems) and each subsystem consists of three to four modules (e.g., evaluation condition setup, evaluation experimentation, and textile database management modules) depending on its functional requirements. The affective quality evaluation subsystem was designed to help administer an experiment in a systematic manner and present acoustic and visual stimuli simultaneously in various gait conditions (walking, jogging, and running) to mimic a more realistic situation of textile frictional sound production. Next, the affective quality estimation subsystem was designed to estimate the sound characteristics, affective qualities, overall psychological satisfaction, and reference cluster of a textile using its mechanical and/or sound characteristic information. Lastly, the audible distance estimation subsystem was designed to estimate the just noticeable sound pressure levels and audible distances of a textile for various gait conditions using its mechanical characteristic information. The AQEEST can be upgraded by accommodating more affective quality study results for various textiles.