Physical Properties Of Stimuli Research Articles

Variability of pulse width in transcranial magnetic stimulation

Objective. There is a high variability in the physiological effects of transcranial magnetic brain stimulation, resulting in limited generalizability of measurements. The cause of the variability is assumed to be primarily based on differences in brain function and structure of the stimulated individuals, while the variability of the physical properties of the magnetic stimulus has so far been largely neglected. Thus, this study is dedicated to the systematic investigation of variability in the pulse width of different TMS pulse sources at different stimulation intensities. Approach. The pulse widths of seven MagVenture® pulse sources were measured at the output of 10%–100% stimulation intensity in 10% increments via Near Field Probe and oscilloscope. The same C-B60 coil was used to deliver biphasic pulses. Pulse widths were compared between pulse sources and stimulation intensities. Main results. The mean sample pulse width was 288.11 ± 0.37 µs, which deviates from the value of 280 µs specified by the manufacturer. The pulse sources and stimulation intensities differ in their average pulse width (p’s < .001). However, the coefficient of variation within the groups (pulse source; stimulation intensity) were moderately low (CV = 0.13%–0.67%). Significance. The technical parameter of pulse width shows deviations from the proposed manufacturer value. According to our data, within a pulse source of the same manufacturer, the pulse width variability is minimal, but varies between pulse sources of the same and other pulse source models. Whether the observed variability in pulse width has potential physiological relevance was tested in a pilot experiment on a single healthy subject, showing no significant difference in motor evoked potential amplitude and significant difference in latencies. Future research should systematically investigate the physiological effects of different pulse lengths. Furthermore, potential hardware ageing effects and pulse amplitude should be investigated.

Validation of scrambling methods for vocal affect bursts

Studies on perception and cognition require sound methods allowing us to disentangle the basic sensory processing of physical stimulus properties from the cognitive processing of stimulus meaning. Similar to the scrambling of images, the scrambling of auditory signals is aimed at creating stimulus instances that are unrecognizable but have comparable low-level features. In the present study, we generated scrambled stimuli of short vocalizations taken from the Montreal Affective Voices database (Belin et al., Behav Res Methods, 40(2):531–539, 2008) by applying four different scrambling methods (frequency-, phase-, and two time-scrambling transformations). The original stimuli and their scrambled versions were judged by 60 participants for the apparency of a human voice, gender, and valence of the expressions, or, if no human voice was detected, for the valence of the subjective response to the stimulus. The human-likeness ratings were reduced for all scrambled versions relative to the original stimuli, albeit to a lesser extent for phase-scrambled versions of neutral bursts. For phase-scrambled neutral bursts, valence ratings were equivalent to those of the original neutral burst. All other scrambled versions were rated as slightly unpleasant, indicating that they should be used with caution due to their potential aversiveness.

2MDR, a Microcomputer-Controlled Visual Stimulation Device for Psychotherapy-Like Treatments of Mice.

Post-traumatic stress disorder and other mental disorders can be treated by an established psychotherapy called Eye Movement Desensitization and Reprocessing (EMDR). In EMDR, patients are confronted with traumatic memories while they are stimulated with alternating bilateral stimuli (ABS). How ABS affects the brain and whether ABS could be adapted to different patients or mental disorders is unknown. Interestingly, ABS reduced conditioned fear in mice. Yet, an approach to systematically test complex visual stimuli and compare respective differences in emotional processing based on semiautomated/automated behavioral analysis is lacking. We developed 2MDR (MultiModal Visual Stimulation to Desensitize Rodents), a novel, open-source, low-cost, customizable device that can be integrated in and transistor-transistor logic (TTL) controlled by commercial rodent behavioral setups. 2MDR allows the design and precise steering of multimodal visual stimuli in the head direction of freely moving mice. Optimized videography allows semiautomatic analysis of rodent behavior during visual stimulation. Detailed building, integration, and treatment instructions along with open-source software provide easy access for inexperienced users. Using 2MDR, we confirmed that EMDR-like ABS persistently improves fear extinction in mice and showed for the first time that ABS-mediated anxiolytic effects strongly depend on physical stimulus properties such as ABS brightness. 2MDR not only enables researchers to interfere with mouse behavior in an EMDR-like setting, but also demonstrates that visual stimuli can be used as a noninvasive brain stimulation to differentially alter emotional processing in mice.

Social context modulates autonomic responses to direct eye contact

Eye contact with another person (social gaze) can evoke emotions, produce autonomic arousal, and influence behavior. Gaze cues can be evocative even when presented in static pictures of faces suggesting that responses depend on low-level visual features of gaze stimuli. The current study examined whether emotional gaze responses depend on the physical stimulus properties of an eye contact experience versus the cognitive evaluation of the social context of gaze. This was done by comparing skin conductance responses (SCR), an index of emotional arousal, during episodes of social gaze and 'self-gaze' (gazing at one's own eyes in a mirror), keeping other aspects of the viewing conditions constant. We compared SCRs during social gaze and self-gaze in forty participant pairs. Each participant engaged in ten, 20 second eye contact trials, alternating between social and self-gaze. Self-gaze episodes produced significant SCRs but social gaze SCR's were larger and occurred more reliably. SCRs decreased across trials (habituation effect) in both conditions. We speculated that social gaze between opposite sex partners might yield larger SCRs but this was not found. Overall, these results conceptually replicate previous findings of (likely top-town) cognitive regulation of autonomic gaze responses based on evaluation of the social context.

Hierarchical unimodal processing within the primary somatosensory cortex during a bimodal detection task

Do sensory cortices process more than one sensory modality?To answer these questions, scientists have generated a wide variety of studies at distinct space-time scales in different animal models, and often shown contradictory conclusions. Some conclude that this process occurs in early sensory cortices, but others that this occurs in areas central to sensory cortices. Here, we sought to determine whether sensory neurons process and encode physical stimulus properties of different modalities (tactile and acoustic). Forthis, we designed a bimodal detection task where the senses of touch and hearing compete from trial to trial. Two Rhesus monkeys performed this novel task, while neural activity was recorded in areas 3b and 1 of the primary somatosensory cortex (S1). Weanalyzed neurons' coding properties and variability, organizing them by their receptive field's position relative to the stimulation zone. Our results indicate that neurons of areas 3b and 1 are unimodal, encoding only the tactile modality in both the firing rate and variability. Moreover, we found that neurons in area 3b carried more information about the periodic stimulus structure than those in area 1, possessed lower response and coding latencies, and had a lower intrinsic time scale. In sum, these differences reveal a hidden processing-based hierarchy. Finally, using a powerful nonlinear dimensionality reduction algorithm, we show that the activity from areas 3b and 1 can be separated, establishing a clear division in the functionality of these two subareas of S1.

On the encoding of natural music in computational models and human brains.

This article discusses recent developments and advances in the neuroscience of music to understand the nature of musical emotion. In particular, it highlights how system identification techniques and computational models of music have advanced our understanding of how the human brain processes the textures and structures of music and how the processed information evokes emotions. Musical models relate physical properties of stimuli to internal representations called features, and predictive models relate features to neural or behavioral responses and test their predictions against independent unseen data. The new frameworks do not require orthogonalized stimuli in controlled experiments to establish reproducible knowledge, which has opened up a new wave of naturalistic neuroscience. The current review focuses on how this trend has transformed the domain of the neuroscience of music.

Light-stimulus intensity modulates startle reflex habituation in larval zebrafish

The startle reflex in larval zebrafish describes a C-bend of the body occurring in response to sudden, unexpected, stimuli of different sensory modalities. Alterations in the startle reflex habituation (SRH) have been reported in various human and animal models of neurological and psychiatric conditions and are hence considered an important behavioural marker of neurophysiological function. The amplitude, offset and decay constant of the auditory SRH in larval zebrafish have recently been characterised, revealing that the measures are affected by variation in vibratory frequency, intensity, and interstimulus-interval. Currently, no study provides a model-based analysis of the effect of physical properties of light stimuli on the visual SRH. This study assessed the effect of incremental light-stimulus intensity on the SRH of larval zebrafish through a repeated-measures design. Their total locomotor responses were normalised for the time factor, based on the behaviour of a (non-stimulated) control group. A linear regression indicated that light intensity positively predicts locomotor responses due to larger SRH decay constants and offsets. The conclusions of this study provide important insights as to the effect of light properties on the SRH in larval zebrafish. Our methodology and findings constitute a relevant reference framework for further investigation in translational neurophysiological research.

Adaptive current-flow models of ECT: Explaining individual static impedance, dynamic impedance, and brain current density

BackgroundImprovements in electroconvulsive therapy (ECT) outcomes have followed refinement in device electrical output and electrode montage. The physical properties of the ECT stimulus, together with those of the patient's head, determine the impedances measured by the device and govern current delivery to the brain and ECT outcomes. ObjectiveHowever, the precise relations among physical properties of the stimulus, patient head anatomy, and patient-specific impedance to the passage of current are long-standing questions in ECT research and practice. To this end, we develop a computational framework based on diverse clinical data sets. MethodsWe developed anatomical MRI-derived models of transcranial electrical stimulation (tES) that included changes in tissue conductivity due to local electrical current flow. These “adaptive” models simulate ECT both during therapeutic stimulation using high current (∼1 A) and when dynamic impedance is measured, as well as prior to stimulation when low current (∼1 mA) is used to measure static impedance. We modeled two scalp layers: a superficial scalp layer with adaptive conductivity that increases with electric field up to a subject-specific maximum (σSS¯), and a deep scalp layer with a subject-specific fixed conductivity (σDS). ResultsWe demonstrated that variation in these scalp parameters may explain clinical data on subject-specific static impedance and dynamic impedance, their imperfect correlation across subjects, their relationships to seizure threshold, and the role of head anatomy. Adaptive tES models demonstrated that current flow changes local tissue conductivity which in turn shapes current delivery to the brain in a manner not accounted for in fixed tissue conductivity models. ConclusionsOur predictions that variation in individual skin properties, rather than other aspects of anatomy, largely govern the relationship between static impedance, dynamic impedance, and ECT current delivery to the brain, themselves depend on assumptions about tissue properties. Broadly, our novel modeling pipeline opens the door to explore how adaptive-scalp conductivity may impact transcutaneous electrical stimulation (tES).

Pictorial low-level features in mental images: evidence from eye fixations.

It is known that eye movements during object imagery reflect areas visited during encoding. But will eye movements also reflect pictorial low-level features of imagined stimuli? In this paper, three experiments are reported in which we investigate whether low-level properties of mental images elicit specific eye movements. Based on the conceptualization of mental images as depictive representations, we expected low-level visual features to influence eye fixations during mental imagery, in the absence of a visual input. In a first experiment, twenty-five participants performed a visual imagery task with high vs. low spatial frequency and high vs. low contrast gratings. We found that both during visual perception and during mental imagery, first fixations were more often allocated to the low spatial frequency-high contrast grating, thus showing that eye fixations were influenced not only by physical properties of visual stimuli but also by its imagined counterpart. In a second experiment, twenty-two participants imagined high contrast and low contrast stimuli that they had not encoded before. Again, participants allocated more fixations to the high contrast mental images than to the low contrast mental images. In a third experiment, we ruled out task difficulty as confounding variable. Our results reveal that low-level visual features are represented in the mind's eye and thus, they contribute to the characterization of mental images in terms of how much perceptual information is re-instantiated during mental imagery.

Why Are Acquired Search-Guiding Context Memories Resistant to Updating?

Looking for goal-relevant objects in our various environments is one of the most ubiquitous tasks the human visual system has to accomplish (Wolfe, 1998). Visual search is guided by a number of separable selective-attention mechanisms that can be categorized as bottom-up driven – guidance by salient physical properties of the current stimuli – or top-down controlled – guidance by observers' “online” knowledge of search-critical object properties (e.g., Liesefeld and Müller, 2019). In addition, observers' expectations based on past experience also play also a significant role in goal-directed visual selection. Because sensory environments are typically stable, it is beneficial for the visual system to extract and learn the environmental regularities that are predictive of (the location of) the target stimulus. This perspective article is concerned with one of these predictive mechanisms: statistical context learning of consistent spatial patterns of target and distractor items in visual search. We review recent studies on context learning and its adaptability to incorporate consistent changes, with the aim to provide new directions to the study of processes involved in the acquisition of search-guiding context memories and their adaptation to consistent contextual changes – from a three-pronged, psychological, computational, and neurobiological perspective.

Cortical fNIRS Responses Can Be Better Explained by Loudness Percept than Sound Intensity.

Functional near-infrared spectroscopy (fNIRS) is a brain imaging technique particularly suitable for hearing studies. However, the nature of fNIRS responses to auditory stimuli presented at different stimulus intensities is not well understood. In this study, we investigated whether fNIRS response amplitude was better predicted by stimulus properties (intensity) or individually perceived attributes (loudness). Twenty-two young adults were included in this experimental study. Four different stimulus intensities of a broadband noise were used as stimuli. First, loudness estimates for each stimulus intensity were measured for each participant. Then, the 4 stimulation intensities were presented in counterbalanced order while recording hemoglobin saturation changes from cortical auditory brain areas. The fNIRS response was analyzed in a general linear model design, using 3 different regressors: a non-modulated, an intensity-modulated, and a loudness-modulated regressor. Higher intensity stimuli resulted in higher amplitude fNIRS responses. The relationship between stimulus intensity and fNIRS response amplitude was better explained using a regressor based on individually estimated loudness estimates compared with a regressor modulated by stimulus intensity alone. Brain activation in response to different stimulus intensities is more reliant upon individual loudness sensation than physical stimulus properties. Therefore, in measurements using different auditory stimulus intensities or subjective hearing parameters, loudness estimates should be examined when interpreting results.

How does the non-conscious become conscious?

In this My Word, Joseph LeDoux describes how his work as a graduate student got him interested in human consciousness. Although he has not studied this topic since 1970s, he never stopped thinking and writing about it during his four-decade career exploring how non-conscious processes involving the amygdala detect and respond to danger. Here, he tells us what is on his mind about consciousness these days.

Odor Stimuli: Not Just Chemical Identity.

In most sensory modalities the underlying physical phenomena are well understood, and stimulus properties can be precisely controlled. In olfaction, the situation is different. The presence of specific chemical compounds in the air (or water) is the root cause for perceived odors, but it remains unknown what organizing principles, equivalent to wavelength for light, determine the dimensions of odor space. Equally important, but less in the spotlight, odor stimuli are also complex with respect to their physical properties, including concentration and time-varying spatio-temporal distribution. We still lack a complete understanding or control over these properties, in either experiments or theory. In this review, we will concentrate on two important aspects of the physical properties of odor stimuli beyond the chemical identity of the odorants: (1) The amplitude of odor stimuli and their temporal dynamics. (2) The spatio-temporal structure of odor plumes in a natural environment. Concerning these issues, we ask the following questions: (1) Given any particular experimental protocol for odor stimulation, do we have a realistic estimate of the odorant concentration in the air, and at the olfactory receptor neurons? Can we control, or at least know, the dynamics of odorant concentration at olfactory receptor neurons? (2) What do we know of the spatio-temporal structure of odor stimuli in a natural environment both from a theoretical and experimental perspective? And how does this change if we consider mixtures of odorants? For both topics, we will briefly summarize the underlying principles of physics and review the experimental and theoretical Neuroscience literature, focusing on the aspects that are relevant to animals’ physiology and behavior. We hope that by bringing the physical principles behind odor plume landscapes to the fore we can contribute to promoting a new generation of experiments and models.

Visual Search Performance and Strategy for Three-Dimensional Visualization Systems: Impact of Radiologist Experience

The visual search performance of radiologists is systematically challenged due to the use of flat-panel displays when viewing multi-slice images. Three-dimensional visualization of information is expected to facilitate visual search for radiologists. However, as the differences in user performance, depending on radiologist experience, have not yet been assessed for real three-dimensional images, it is difficult to estimate the usability of new visualization systems for radiologists with different amounts of professional search experience. In this study, we aimed to determine how three-dimensional visual search is affected by radiologist experience and the physical properties of stimuli. Radiologists, residents, and medical students accomplished visual search tasks with varying set sizes and target-distractor similarities. Search items were presented on multiple display planes and image manipulation was conducted using a computer keyboard. We compared the search outcome and strategy among three groups of participants. All three groups submitted a similar number of correct responses depending on target-distractor similarity. However, in contrast to radiologists and residents, it took a considerably longer time for students to find the targets. The major differences were evident in search strategy when comparing the image manipulations of radiologists with those of residents and students. Our results demonstrated that experienced radiologists’ search performance benefited from seeing the entire three-dimensional view of an image, whereas residents and students focused instead on reducing the amount of information and searched in a selective manner. These findings should be taken into account when planning the implementation of new workstations with three-dimensional visualization in radiology.

Enhanced processing of facial emotion for target stimuli

It is as yet unresolved to what extent the pre-attentive detection of auditory deviance is modulated by emotion. The current event-related potential study was designed to investigate simultaneously the auditory and the visual mismatch negativity (MMN), as well as the impact of emotion on the auditory MMN. Thirty healthy participants saw sequences of neutral and fearful face stimuli and were instructed to identify easily detectable target faces by button press, whereas simultaneously presented auditory stimuli did not require any behavioral response. Increased N170 and N250 amplitudes to fearful faces indicated a differential processing of the fearful and neutral faces as standards. A visual MMN was clearly elicited by fearful face deviants, but hardly by neutral face deviants. Neither the auditory MMN nor the processing of visual targets was modulated by the facial emotion. However, the N250 modulation by emotion was surprisingly larger in target than in non-target trials. Findings suggest that the pre-attentive detection of auditory deviance as reflected in the auditory MMN is not substantially modulated by emotion induced by visual stimulation. The wide lack of a significant visual MMN to neutral deviants indicates that this deviance detection is not driven by physical stimulus properties (because otherwise the visual MMN to fearful and neutral deviants should have the same magnitude) but strongly by the emotional significance. The behavioral significance of targets apparently led to an enhanced processing of emotional features even though these features were irrelevant for target detection task.

The use of stimulus perception to account for variability in skin conductance responses to interoceptive stimuli.

Activity of the electrodermal response system is customarily expressed in relation to physical stimulus properties and not to perceived features. In situations where the delivery of physically identical stimuli can be challenging, such as in interoception research, this variability might pose a challenge for contemporary SCR analyses. Therefore, we investigated the extent to which activity in the electrodermal response system triggered by the delivery of interoceptive stimuli is better predicted by perceived intensity rather than physical input. For this purpose, we reanalyzed data from the baseline phase of a previous study (n=60) in which skin conductance responses (SCRs) to innocuous esophageal stimulations of high and low intensities were recorded in addition to categorizations based on their perceived intensity (high or low). Using both peak scoring and model inversion methods, we found that the inclusion of stimulus perception as a predictor of the magnitude of the SCR increased model fit. These findings suggest that the inclusion of perception is a promising avenue to better model variability in psychophysiological responses to interoceptive stimuli.

Enhanced early visual processing after evaluative conditioning

The emotional significance of a stimulus is known to influence attentional selection leading to prioritization even at early stages of visual perception (e.g., selection from iconic memory). However, as the emotional meaning can be confounded with physical stimulus properties, it is possible that the prioritization is not driven by emotional factors alone. Here we use evaluative conditioning to manipulate the emotional meaning of arbitrary visual stimuli by repeatedly pairing each stimulus with either positive, negative, or neutral pictures. The subjective liking of conditioned stimuli (CSs) revealed reliable evaluative conditioning effects. Sensory processing advantages were measured by presenting the CSs in an iconic memory task asking participants to identify a target in a display of briefly presented stimuli. An adaptive variation of exposure durations revealed that shorter durations were required for the recognition of targets that were previously paired with negative or positive images than for neutral targets, indicating prioritized selection of affective CSs from iconic memory. Two additional experiments investigated the subsequent decay of information that was initially available in iconic memory by manipulated the delay of the recognition cue. Results show that positive CSs were more likely to be selected from iconic memory than neutral CSs, whereas negative CSs were prioritized in terms of prolonged availability in iconic memory. Taken together, the findings suggest that the affective learning history leads to prioritization at the level of iconic memory.

Pigeon category learning: Revisiting the Shepard, Hovland, and Jenkins (1961) tasks.

In a seminal study, Shepard, Hovland, and Jenkins (1961; henceforth SHJ) assessed potential mechanisms involved in categorization learning. To do so, they sequentially trained human participants with 6 different visual categorization tasks that varied in structural complexity. Humans' exceptionally strong performance on 1 of these tasks (Type 2, organized around exclusive-or relations) could not be solely explained by structural complexity, and has since been considered the hallmark of rule-use in these tasks. In the present project, we concurrently trained pigeons on all 6 SHJ tasks. Our results revealed that the structural complexity of the tasks was highly correlated with group-level performance. Nevertheless, we observed notable individual differences in performance. Two extensions of a prominent categorization model, ALCOVE (Kruschke, 1992), suggested that disparities in the discriminability of the dimensions used to construct the experimental stimuli could account for these differences. Overall, our pigeons' generally weak performance on the Type 2 task provides no evidence of rule-use on the SHJ tasks. Pigeons thus join monkeys in the contingent of species that solve these categorization tasks solely on the basis of the physical properties of the training stimuli. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Cell Mechanotransduction With Piconewton Forces Applied by Optical Tweezers.

Mechanical stresses are always present in the cellular environment and mechanotransduction occurs in all cells. Although many experimental approaches have been developed to investigate mechanotransduction, the physical properties of the mechanical stimulus have yet to be accurately characterized. Here, we propose a mechanical stimulation method employing an oscillatory optical trap to apply piconewton forces perpendicularly to the cell membrane, for short instants. We show that this stimulation produces membrane indentation and induces cellular calcium transients in mouse neuroblastoma NG108-15 cells dependent of the stimulus strength and the number of force pulses.

Discrimination between smiling faces: Human observers vs. automated face analysis

This study investigated (a) how prototypical happy faces (with happy eyes and a smile) can be discriminated from blended expressions with a smile but non-happy eyes, depending on type and intensity of the eye expression; and (b) how smile discrimination differs for human perceivers versus automated face analysis, depending on affective valence and morphological facial features. Human observers categorized faces as happy or non-happy, or rated their valence. Automated analysis (FACET software) computed seven expressions (including joy/happiness) and 20 facial action units (AUs). Physical properties (low-level image statistics and visual saliency) of the face stimuli were controlled. Results revealed, first, that some blended expressions (especially, with angry eyes) had lower discrimination thresholds (i.e., they were identified as “non-happy” at lower non-happy eye intensities) than others (especially, with neutral eyes). Second, discrimination sensitivity was better for human perceivers than for automated FACET analysis. As an additional finding, affective valence predicted human discrimination performance, whereas morphological AUs predicted FACET discrimination. FACET can be a valid tool for categorizing prototypical expressions, but is currently more limited than human observers for discrimination of blended expressions. Configural processing facilitates detection of in/congruence(s) across regions, and thus detection of non-genuine smiling faces (due to non-happy eyes).