Multisensory

• Assemblies of neurons are transient
• Multisensory integration is the study of how information from the different sensory modalities may be integrated by the nervous system.
• Multisensory interraction : when perception of sensory information is interrupted by presentation of other modalities
• Multisensory congruence : how different sensory information come together in specific brain regions. Criteria are both anatomical and physiolological
• Detectability is the facility from which a signal can be distinguished from noise. You have RT, perception threshold and detection probability
• Perception threshold: the intensity where a subject detects a stimulus in 50% of trials.
• RT of multi sensory intergation is based on 2 hypotheses of models :

  • race/competition model
  • coactivation model
• Race/competition model is when you have the faster stimulus that is responsible for the response, here you have NO multisensory integration
• Covariation model is the best because it is the coactivation of both sensory channels like auditory and visual = aka multisensory integration
• Identification of a stimulus is faster and more precise when the stimulus is bimodal compared to unimodal
• language intelligibility is improved by audiovisual stimuli
• Ventriloquism effect : when a visual stimulus influences the perceived spatial position of an auditory stimulus = aka spatial conflict
• McGurk is the same effect as ventriloquism but this time based on incongruent bimodal stimuli
• In bouncing discs, other sensory modalities increase the bouncing percepton
• Multisensory intergation is basiacally an optima Bayesian integration. It means it can use old information in order to help prediction
• Low-level neural processing is the one based on the primary unimodal areas, meaning the new information
• High-level neural processing is the one based on multisensory areas like parietal, frontal and temporal
• Maximum Likelihood Estimation is another Bayesian model that can combine two or more signals that are weighted in function of their reliability
• haptic = sensory information
• Olfaction is influenced by visual information. The integration is faster and more accruate in the congruent configuration
• Synesthesia is the disorder where senses are mixed up. You can test it with Stroop interference and visual search paradigm
• Sensory information processing in the cortex is a highly hierarchical and segregated
• Visual areas of cortex is composed of medial surface of occipital cortex
• Auditory areas of the cortex is composed of the temporal gyrus
• Tonotopy is the spatial representation of frequencies in A1 that preserves the spatial organization of sound in the cochelea
• In the auditory cortex, if low frequency stimulation then activaiton anterior and medial A1
• In the auditory cortex, if high frequency stimulation then activaiton posterior and lateral A1
• Retinotropy = spatial organization that preserves the correspondence between retinal regions and V1
• Somatosensory cortex is composed of the anterior part of the post-central gyrus
• Le principe de hierarchisation est simple : Une aire est positionnée au-dessus d’une autre si elle reçoit de celle-ci des projections feedforward.
• Multisensory areas in primates you have the STP and VIP
• So in primates, the VIP area is a major site of multiple sensory information
• STP is the superior temporal polysensory area
• In humans, STS is a major site of multisensory convergence.
• Sub-cortical regions are also sites of multisensory convergence (CS, CI, putamen,basal ganglia, amygdala, hippocampus, thalamus).
• SC is the superior colliculus and involved in orientation behavior towards multisensory targets
• Superior colliculus have cells in ?

  • Superficial layer neurons = visual neurons, A spatial maps
  • Deep layer neurons = multisensory neurons, A/V/S spatial maps
• more than a half of the CS (aka the superior colliculus) neurons are multisensorial
• RF : receptive field, is a sensory space within which a neuron or group of neurons responds to stimuli
• bimodal response of the neuron is significantly different from

  the maximal unimodal response meaning ⇒ enhancement response