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PSYC2020 > Week 7 > Flashcards

Week 7 Flashcards

1
Q

Speech in Noise

A 
Vision helps to resolve ambiguity
Few “lip readers”
but visual speech
greatly improves
perception in noise
Automatic
Greater than sum of
parts
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2
Q

Warning Signals

A 
Faster response to multimodal
stimuli
Flashing indicator
Beeping indicator
Flash/Beep
more reliable
faster
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3
Q

Flavour

A 
“Flavour is in the brain”
Taste
Smell
Somatosensory
Modulators
Sight
Sounds
Smells
Expectation
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4
Q

A Unified Perceptual Experience

A

“… it is surely one of the great remaining scientific puzzles just
how it is that signals from such completely separated and
wholly dissimilar sensory epithelia as the haircells of the
cochlea, the photoreceptors of the retina and the corpuscles
of the skin can be integrated centrally to form such a seamless
unitary perceptual world”.
Molholm and Foxe, 2010 (p 1709)

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5
Q

Overview - Perception

A

A primary role of the brain
Decide on best/most appropriate action/behaviour
Survival depends on speed and accuracy
with which an organism can evaluate
external events and properly react to
them
gather, interpret and represent information

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6
Q

What are the 4 Multisensory Perceptions?

A

Light, sound, mechanical and chemicals

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7
Q

what is the role of Multisensory Perception?

A

evaluate external events and properly react
to them
Different modalities can substitute when individually
compromised (eg vision lost in the dark)
• Different fields of operation – touch/smell/taste for up close and
vision/hearing for distance
• Resolve ambiguities – 2 things may sound the same but look
different; boost signal to noise
Multisensory integration enhances our ability to perceive
and understand our environment, enabling us to better
interact with our surroundings

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8
Q

Redundant Targets Effect

A 
Miller (1982)
• Speeded response to either audio (A), visual (V), or
audio-visual (AV) target
Redundant since
additional stimulus
doesn’t provide any
additional
information
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9
Q

what are the two models of redundant target effects?

A
  1. Statistical facilitation - independent (parallel)
    processing
  2. Neural coactivation - integrated signals
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10
Q

Redundant Targets Effect-

Statistical Facilitation

A

Both elements of AV stim processed along
independent channels
• One that reaches output stage first triggers
response
• On average, the time of the winner will be less than
the time for either racer

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11
Q

Redundant Targets Effect-

Neural Coactivation

A

Both components of a redundant signal influence
response on a single trial
• Activation from different channels combine in
satisfying a single criterion for response initiation -
activation builds over time until some criterion is
reached
• Activation builds faster when provided by two
sources rather than one

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12
Q

what is the purpose of redundant target effects?

A

• responses to redundant signals are too fast to be
explained as the faster of two responses to
individual signals
• The easiest way to explain the speed of responses
to redundant signals is to assume that signals
jointly contribute to the process of producing the
response
• Neural Coactivation - MSI

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13
Q

MSI – Key Issue

A

Sensory environment is complex – there are
multiple sources in each modality – eg lots of visual
objects and lots of sounds
• Key function of MSI dissociate between stimuli
from different sources and single source

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14
Q

Factors Influencing MSI

A
  • Temporal Coincidence
  • Spatial Coincidence
  • Temporal patterning
  • Crossmodal correspondence
  • Stored knowledge
  • Context
  • Recent experience
  • Expectation
  • Attention
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15
Q

Factors Influencing MSI- bottom up and subjective

A

Temporal Coincidence
• Spatial Coincidence
• Temporal patterning

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16
Q

Factors Influencing MSI- top-down and subjective

A
  • Stored knowledge
  • Context
  • Recent experience
  • Expectation
  • Attention
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17
Q

Bottom-up Factors

A

Temporal Coincidence – things that happen at the same
time
• Spatial Coincidence – things that happen at the same
place
• Temporal patterning – things that are correlated over
time
Strong cues that stimuli were caused by the same event
and so belong together

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18
Q

Top-down Factors

A

Information that is already present in our brain
influences how crossmodal signals are combined
• Stored knowledge
• Recent experience
• Context
• Expectation
• Attention

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19
Q

Top-down: Context

A 
Stream-bounce; 3 blocks of 200 trials each
Block 1 – all no
sound
Block 2 – mixed
sound/no sound
Block 3 – all no
sound
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20
Q

Top-down: Expectation

A

When are cognitive influences (eg previous response, overall
presence of the tone) impacting
Does expectation lead to an early decision or bias?
Typical S/B – observe entire motion sequence then provide
response – subjective
Want to see how percept evolves

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21
Q

Neuroscience of MSI

A

• Minimum 32 visual, 15 auditory, 8 somatosensory areas
identified in primate cortex
• Body control - proprioception, vestibular, vision, motor
control
• How are individual senses integrated?
• How is a unified perceptual experience created?

22
Q

where are multisensory neurons found?

A

nearly every level in the CNS

23
Q

Superior Colliculus

A 
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
24
Q

Superior Colliculus- Multilayered structure

A

Superficial layers are visual – optic tectum in non-mammals

• Deeper layers are multisensory

25
Superior Colliculus- 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
26
Superior Colliculus- receptive field
a region of sensory space that a sensory | neuron preferentially responds to stimuli in
27
what id teh central role of the Superior Colliculus?
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
28
Multisensory Enhancement
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)
29
3 drivers of Multi sensory (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
30
Spatial rule- unimodal
Visual or auditory alone | Weak response
31
Spatial rule- multimodal
``` Large spatial offset Depressed response – less than just visual (spatial separation of AR40V and AR30V) Smaller spatial offset Unimodal response – just the visual (AR20V) Spatial Coincidence Strong multisensory response (AR10V) ```
32
Temporal Rule- unimodal
``` Visual or auditory alone Weak response (V and A) ```
33
Temporal Rule- multimodal
``` Asynchronous AV Unimodal response of whichever stimulus comes first (A200V and V200A) Simultaneous AV Strong multisensory response (AV0) ```
34
Principle of Inverse Effectiveness
strong and weak stimuli
35
Superior Temporal Sulcus (STS)
• 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
36
where does visual processing occur?
occipital lobe and ventral visual to inferior temporal gyrus
37
where does auditory occur?
superior temporal gyrus
38
where is Wernicke's area?
superior temporal gyrus
39
where is the angular gyrus?
inferior parietal lobe
40
McGurk Effect
vision and speech perception
41
research in STS and the McGurk Effect
• 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
42
STS and the McGurk Effect
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
43
STS and the McGurk Effect- | 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
44
Posterior Parietal Cortex (PPC)
• 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
45
PPC and the Flash/Beep Illusion | 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)
46
PPC and the Flash/Beep Illusion | • 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)
47
PPC and Stream-Bounce
Stream-bounce with TMS over left or right PPC
48
Unisensory Cortex and MSI
• 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
49
Unisensory Cortex and MSI- studies
• 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)
50
Multisensory Integration model
former model- Hierarchical functionally Homogeneous Serial | receptors-> Thalamus-> Primary Sensory Cortex-> Secondary Sensory Cortex-> Association Cortex
51
Multisensory Integration | Key Learnings
• MSI – increase precision, amplifies weak signals and resolve ambiguities • Improved orienting towards, detection and identification of relevant events • Greater than the sum of parts • RTE – neural coactivation = MSI • Key issue – what to bind • Range of bottom-up and top-down factors • Top-down factors and stream-bounce • Multisensory neurons are found at nearly every level in the CNS • SC - Deeper layers are multisensory – A, V, S • MS enhancement – spatial rule, temporal rule, principle of inverse effectiveness • Superior Temporal Sulcus (McGurk) • Posterior Parietal Cortex (Flash-Beep and StreamBounce) • Cross-modal modulations of low level unisensory • Integrated, interconnected, feedforward, feedback

PSYC2020 (14 decks)

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