An LCD tachistoscope with submillisecond precision

Tachistoscopes allow brief visual stimulation delivery, which is crucial for experiments in which subliminal presentation is required. Up to now, tachistoscopes have had shortcomings with respect to timing accuracy, reliability, and flexibility of use. Here, we present a new and inexpensive two-channel tachistoscope that allows for exposure durations in the submillisecond range with an extremely high timing accuracy. The tachistoscope consists of two standard liquid-crystal display (LCD) monitors of the light-emitting diode (LED) backlight type, a semipermeable mirror, a mounting rack, and an experimental personal computer (PC). The monitors have been modified to provide external access to the LED backlights, which are controlled by the PC via the standard parallel port. Photodiode measurements confirmed reliable operation of the tachistoscope and revealed switching times of 3 μs. Our method may also be of great advantage in single-monitor setups, in which it allows for manipulating the stimulus timing with submillisecond precision in many experimental situations. Where this is not applicable, the monitor can be operated in standard mode by disabling the external backlight control instantaneousl

The Behavioral Relevance of Multisensory Neural Response Interactions

Sensory information can interact to impact perception and behavior. Foods are appreciated according to their appearance, smell, taste and texture. Athletes and dancers combine visual, auditory, and somatosensory information to coordinate their movements. Under laboratory settings, detection and discrimination are likewise facilitated by multisensory signals. Research over the past several decades has shown that the requisite anatomy exists to support interactions between sensory systems in regions canonically designated as exclusively unisensory in their function and, more recently, that neural response interactions occur within these same regions, including even primary cortices and thalamic nuclei, at early post-stimulus latencies. Here, we review evidence concerning direct links between early, low-level neural response interactions and behavioral measures of multisensory integration

Early, Low-Level Auditory-Somatosensory Multisensory Interactions Impact Reaction Time Speed

Several lines of research have documented early-latency non-linear response interactions between audition and touch in humans and non-human primates. That these effects have been obtained under anesthesia, passive stimulation, as well as speeded reaction time tasks would suggest that some multisensory effects are not directly influencing behavioral outcome. We investigated whether the initial non-linear neural response interactions have a direct bearing on the speed of reaction times. Electrical neuroimaging analyses were applied to event-related potentials in response to auditory, somatosensory, or simultaneous auditory–somatosensory multisensory stimulation that were in turn averaged according to trials leading to fast and slow reaction times (using a median split of individual subject data for each experimental condition). Responses to multisensory stimulus pairs were contrasted with each unisensory response as well as summed responses from the constituent unisensory conditions. Behavioral analyses indicated that neural response interactions were only implicated in the case of trials producing fast reaction times, as evidenced by facilitation in excess of probability summation. In agreement, supra-additive non-linear neural response interactions between multisensory and the sum of the constituent unisensory stimuli were evident over the 40–84 ms post-stimulus period only when reaction times were fast, whereas subsequent effects (86–128 ms) were observed independently of reaction time speed. Distributed source estimations further revealed that these earlier effects followed from supra-additive modulation of activity within posterior superior temporal cortices. These results indicate the behavioral relevance of early multisensory phenomena

Hodger Sperdin, Département de psychiatrie de la Facutlé de médecine de l'UNIGE

Hodger Sperdin, Département de psychiatrie de la Facutlé de médecine de l'UNIG

Single-Trial Multisensory Learning and Memory Retrieval

This chapter reviews our research investigating how the processing of unisensory visual objects is impacted by past experiences with multisensory auditory–visual versions of these objects. Single-trial exposure to multisensory objects during an orthogonal old/new discrimination task can incidentally modulate memory performance as well as brain activity. Performance was enhanced when the preceding multisensory stimulus had been a semantically congruent pairing, whereas performance was impaired by pairings with meaningless pure tones. Importantly, these opposing effects occurred despite identical performance patterns with the initial exposure to the objects (and presumably encoding thereof). In terms of brain activity, responses were enhanced to visual stimuli that had been previously encountered in a multisensory context within regions of the lateral occipital cortex beginning just 60 ms post-stimulus onset. Our collective findings indicate that single-trial learning of multisensory object associations occurs incidentally, is distinguishable from encoding processes, persists despite many intervening stimuli, and manifests as differential brain activity at early processing stages within visual cortices. The consequences of multisensory interactions thus persist over time to impact memory retrieval and object discrimination

Aberrant Development of Speech Processing in Young Children with Autism: New Insights from Neuroimaging Biomarkers

From the time of birth, a newborn is continuously exposed and naturally attracted to human voices, and as he grows, he becomes increasingly responsive to these speech stimuli, which are strong drivers for his language development and knowledge acquisition about the world. In contrast, young children with autism spectrum disorder (ASD) are often insensitive to human voices, failing to orient and respond to them. Failure to attend to speech in turn results in altered development of language and social-communication skills. Here, we review the critical role of orienting to speech in ASD, as well as the neural substrates of human voice processing. Recent functional neuroimaging and electroencephalography studies demonstrate that aberrant voice processing could be a promising marker to identify ASD very early on. With the advent of refined brain imaging methods, coupled with the possibility of screening infants and toddlers, predictive brain function biomarkers are actively being examined and are starting to emerge. Their timely identification might not only help to differentiate between phenotypes, but also guide the clinicians in setting up appropriate therapies, and better predicting or quantifying long-term outcome

Auditory-somatosensory multisensory interactions in humans: dissociating detection and spatial discrimination.

Simple reaction times (RTs) to auditory-somatosensory (AS) multisensory stimuli are facilitated over their unisensory counterparts both when stimuli are delivered to the same location and when separated. In two experiments we addressed the possibility that top-down and/or task-related influences can dynamically impact the spatial representations mediating these effects and the extent to which multisensory facilitation will be observed. Participants performed a simple detection task in response to auditory, somatosensory, or simultaneous AS stimuli that in turn were either spatially aligned or misaligned by lateralizing the stimuli. Additionally, we also informed the participants that they would be retrogradely queried (one-third of trials) regarding the side where a given stimulus in a given sensory modality was presented. In this way, we sought to have participants attending to all possible spatial locations and sensory modalities, while nonetheless having them perform a simple detection task. Experiment 1 provided no cues prior to stimulus delivery. Experiment 2 included spatially uninformative cues (50% of trials). In both experiments, multisensory conditions significantly facilitated detection RTs with no evidence for differences according to spatial alignment (though general benefits of cuing were observed in Experiment 2). Facilitated detection occurs even when attending to spatial information. Performance with probes, quantified using sensitivity (d'), was impaired following multisensory trials in general and significantly more so following misaligned multisensory trials. This indicates that spatial information is not available, despite being task-relevant. The collective results support a model wherein early AS interactions may result in a loss of spatial acuity for unisensory information

Aberrant development of speech processing in young children with autism: new insights from neuroimaging biomarkers

From the time of birth, a newborn is continuously exposed and naturally attracted to human voices, and as he grows, he becomes increasingly responsive to these speech stimuli, which are strong drivers for his language development and knowledge acquisition about the world. In contrast, young children with autism spectrum disorder (ASD) are often insensitive to human voices, failing to orient and respond to them. Failure to attend to speech in turn results in altered development of language and social-communication skills. Here, we review the critical role of orienting to speech in ASD, as well as the neural substrates of human voice processing. Recent functional neuroimaging and electroencephalography studies demonstrate that aberrant voice processing could be a promising marker to identify ASD very early on. With the advent of refined brain imaging methods, coupled with the possibility of screening infants and toddlers, predictive brain function biomarkers are actively being examined and are starting to emerge. Their timely identification might not only help to differentiate between phenotypes, but also guide the clinicians in setting up appropriate therapies, and better predicting or quantifying long-term outcome

An LCD tachistoscope with submillisecond precision

Tachistoscopes allow brief visual stimulation delivery, which is crucial for experiments in which subliminal presentation is required. Up to now, tachistoscopes have had shortcomings with respect to timing accuracy, reliability, and flexibility of use. Here, we present a new and inexpensive two-channel tachistoscope that allows for exposure durations in the submillisecond range with an extremely high timing accuracy. The tachistoscope consists of two standard liquid-crystal display (LCD) monitors of the light-emitting diode (LED) backlight type, a semipermeable mirror, a mounting rack, and an experimental personal computer (PC). The monitors have been modified to provide external access to the LED backlights, which are controlled by the PC via the standard parallel port. Photodiode measurements confirmed reliable operation of the tachistoscope and revealed switching times of 3 μs. Our method may also be of great advantage in single-monitor setups, in which it allows for manipulating the stimulus timing with submillisecond precision in many experimental situations. Where this is not applicable, the monitor can be operated in standard mode by disabling the external backlight control instantaneously

Neural processing of dynamic animated social interactions in young children with autism spectrum disorder: a high-density electroencephalography study

Background: Atypical neural processing of social visual information contributes to impaired social cognition in autism spectrum disorder. However, evidence for early developmental alterations in neural processing of social contingencies is scarce. Most studies in the literature have been conducted in older children and adults. Here, we aimed to investigate alterations in neural processing of social visual information in children with autism spectrum disorder compared to age-matched typically developing peers. Methods: We used a combination of 129-channel electroencephalography and high-resolution eye-tracking to study differences in the neural processing of dynamic cartoons containing human-like social interactions between 14 male children with autism spectrum disorder and 14 typically developing male children, aged 2-5 years. Using a microstate approach, we identified four prototypical maps in both groups and compared the temporal characteristics and inverse solutions (activation of neural sources) of these maps between groups. Results: Inverse solutions of the group maps that were most dominant during free viewing of the dynamic cartoons indicated decreased prefrontal and cingulate activation, impaired activation of the premotor cortex, and increased activation of parietal, temporal, occipital, and cerebellar regions in children with autism spectrum disorder compared to their typically developing peers. Conclusions: Our findings suggest that impairments in brain regions involved in processing social contingencies embedded in dynamic cartoons are present from an early age in autism spectrum disorder. To the best of our knowledge, this is the first study to investigate neural processing of social interactions of children with autism spectrum disorder using dynamic semi-naturalistic stimuli