Week 7 Flashcards

Question

Superior Colliculus

Answer 1

• Reflexive orienting to stimuli in contralateral space • Produces motor actions that are guided by sensory stimuli • Converging visual, auditory and somatosensory projections from numerous cortical and subcortical sources • Inputs – retina, cortex, IC, spinal cord • Outputs – motor control of eyes, ears and head • Multilayered structure • Superficial layers are visual – optic tectum in non-mammals • Deeper layers are multisensory • MS cells • Inputs from 2 or more sensory systems – A/V, V/S, A/V/S • Overlapping receptive fields • Can respond to single sensory input – but weakly • Preferentially (stronger) response to multiple inputs • Receptive field – a region of sensory space that a sensory neuron preferentially responds to stimuli in • Central role in integration of info from different modalities and generation of spatial orienting responses • Important as a MS structure, but also good as a general model of MSI • Early cellular neurobiology work by Stein et al • Single cell recordings – MS cells in SC of cats

Answer 2

MS neurons – response to appropriate multisensory stimuli exceeds the response to individual unisensory inputs and can even exceed the sum of the unisensory inputs (super-additivity) But – get suppression of inappropriate (incoherent or misaligned) stimuli (sub-additivity) 3 drivers of MS enhancement or super-additivity: 1. Spatial rule MS stimuli must occur at the same region of space 2. Temporal rule MS stimuli must reach the MS cell at the same time 3. Principle of Inverse effectiveness Enhancement is greater for weak stimuli than strong

Answer 3

Unimodal Visual or auditory alone Weak response

Answer 4

``` Multimodal Large spatial offset Depressed response – less than just visual Smaller spatial offset Unimodal response – just the visual Spatial Coincidence Strong multisensory response ```

Answer 5

Unimodal Visual or auditory alone Weak response

Answer 6

``` Multimodal Asynchronous AV Unimodal response of whichever stimulus comes first Simultaneous AV Strong multisensory response ```

Answer 7

• STS as a region involved in audio–visual speech processing • STS may be generally involved in binding auditory and visual inputs, regardless of whether they contain speech or biological motion

Answer 8

• Beauchamp et al. (2010) • Use fMRI to identify MS area – left posterior STS responded to both auditory and visual speech • Show mismatched AV speech (McGurk) with and without TMS of Left STS • Control 1 – auditory only with and without TMS – check if effect is speech in general or MSI • Control 2 – TMS of second site 1. No TMS – mostly illusion 2. TMS of left STS - illusion down to 50% of trials 3. Control 1 – TMS and auditory only – no effect on speech perception 4. Control 2 – TMS of second site – no effect on McGurk susceptibility Plasticity • Stroke patient with ablated left posterior STS • Recovery and rehab reported good understanding of speech but it was effortful • Report experiencing McGurk effect • Right STS activation and larger volume than age matched controls

Answer 9

• PPC plays a critical role in functions related to attention allocation for unimodal and multisensory processing • Reference frame remapping by the PPC may be critical for aligning inputs to facilitate integration • PPC is also ideally situated to mediate interactions between the sensory systems by shaping processing in primary sensory areas via feedback projections • anodal tDCS speeds reaction times for detecting auditory, visual and bimodal auditory–visual targets when applied over right PPC

Answer 10

• Flash/Beep (Shams et al. (2002): single flash of light with multiple beeps • Sound induced illusory flashing - Report 2 or more flashes when 2 or more beeps (fission) • Kamke et al (2012) • Illusory flash perception is typically only reported on a proportion of trials suggesting that stimulus characteristics alone do not determine the illusory percept TMS to one of 2 PPC areas (angular gyrus and supramarginal gyrus) or S1 (control)

Answer 11

• Also modulation of low-level sensory cortex by other modalities • Human fMRI studies by Calvert et al. found that the substantial improvement of auditory speech perception when the speaker’s face was visible was accompanied by a significant response enhancement in auditory cortex • Romei et al. demonstrated that auditory stimulation can decrease the threshold of perceived phosphene induced by a single pulse TMS applied over the occipital pole • Single flash being misperceived as two with two beeps accompanies an enhancement of visual activity in V1 (Watkins et al., 2006) • Double flash being misperceived as a single flash due to a single beep relates to a decrease in V1 activity (Watkins et al., 2007) • ERP work showing interactions between auditory and visual stimuli at very short latency (46ms to 150ms)