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perception- year 3 > lecture 4- multisensory perception & the sense of body ownership > Flashcards

lecture 4- multisensory perception & the sense of body ownership Flashcards

1
Q

perception is..

A

multisensory in natural interactions with the environment

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2
Q

information from different senses can either be..

A

complementary or redundant/overlapping

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3
Q

what does multisensory information increase?

A

increases reliability of the percept and provides a more complete representation of the world (+ increases resistance to interference)

note: [note: vast amount of research on all senses and their possible interactions – here focus on vision & touch and audition & touch]

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4
Q

multisensory:

A

more than one modality is used in perception

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5
Q

cross-modal:

A

interactions between different modalities=> one sense affects perceptions provided by a different sense

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6
Q

integration:

A

merging information from different modalities into a unified percept

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6
Q

multisensory perception

A
  • Different modalities can provide convergent information about the same external event/properties
  • CNS has to disentangle cases where stimulation of different senses is unrelated and where it is related
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7
Q

simple heuristics for integration:

A
  • temporal correlation
  • spatial congruency
  • inverse effectiveness
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7
Q

temporal correlation:

A

Stimulation of different modalities occurs at
(roughly) the same time

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8
Q

spatial congruency:

A

Stimuli in the different senses come from
approximately the same location

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9
Q

inverse effectiveness:

A

Reduced benefit of multisensory integration the stronger the unimodal signal of a cross-modal cue → Multisensory response is stronger when one stimulus by itself is quite weak

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10
Q

inverse effectiveness: single neuron II:

A
  • superaddictivity
  • additivity
  • subadditivity
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10
Q

inverse effectiveness: single neuron I- multi-modal neurons in superior colliculus (SC) (relevant for rapid orienting of attention):

A
  • Spikes produced by combination of visual and auditory event (5) is larger than the individual neural spikes in response to visual (1) and auditory stimuli (2)
  • Superadditivity of spike counts:
    Multisensory response is greater than the sum of uni-sensory responses
  • Sum usually only larger for weak inputs (near threshold) → aids detection of weak stimuli → speeds up behavioural responses
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11
Q

Additivity:

A

As cues become stronger unisensory
responses become stronger → integrated response is not different from the sum of the responses to each component

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12
Q

Superadditivity:

A

Both cues are weak – response
exceeds the sum of the separate inputs

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13
Q

Subadditivity:

A

Combined input is smaller than the
sum of the two uni-sensory inputs (but still
exceeds the largest single input response)

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14
Q

Definition: Inverse Effectiveness

A

Degree to which a multisensory response exceeds the response of the most effective modality specific stimulus component declines as the effectiveness of the modality-specific stimulus component increases

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15
Q

neural mechanisms- subcortical areas:

A

Superior colliculus

  • Located in the mid-brain – important for orienting behaviour and fast motor
    reactions
  • High(est) proportion of multisensory neurons (extensively studied)
  • Neurons show overlapping
    spatial maps for visual, auditory
    and somatosensory modalities
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16
Q

neural mechanisms- cortical areas

A
  • Multisensory neurons are
    found in most areas – often in combination
    with unimodal neurons
  • Even in areas previously considered modality specific (e.g., neurons in visual cortex respond to tactile cues, and neurons in
    primary auditory cortex are activated by
    visual lip movements)
  • Studies in primates primarily focussed on
    posterior parietal cortex (converging
    information from visual, vestibular, tactile
    and auditory system)
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17
Q

cross-modal integration

A
  • How is input from two senses combined perceptually?
  • Different modalities are combined to yield the best estimate of the external properties
  • The modality that provides more reliable information is given more weight (greater reduction in uncertainty)

→ e.g., vision strongly influences auditory localisation (ventriloquist effect) – vision is spatially more accurate

→ audition can dominate vision in temporal properties, e.g., auditory flutter drives perception of visual flicker
→ Modality appropriateness hypothesis

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18
Q

interim summary I

A
  • 3 simple heuristics of multi-sensory integration
  • Inverse Effectiveness in multisensory neurons of the SC
  • Weighing of different stimuli depends on their accuracy and reliability
  • Role of semantic congruency in strengthening multisensory integration
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18
Q

semantic congruency

A
  • Semantic congruency (consistent
    meaning of two stimuli) strengthens
    multisensory stimulus integration and
    corresponding behavioural performance
  • Semantic congruency of visual and
    auditory stimuli affects the speed of
    participants responses → faster target detections when visual stimulus is accompanied by a semantically congruent sound
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19
Q

crossmodal illusions

A

REMINDER

  • Complementary information improves
    the reliability of our perception
  • Incongruent information can result in
    unexpected percepts due to sensory
    interactions (e.g., audio-visual illusion
    of the McGurk Effect)
  • Less research on multisensory illusions
    including the tactile domain – e.g.,
    audio-tactile interactions (noise bursts
    can affect perception of roughness)
20
Q

parchment skin illusion:

A

(1998, Jousmaeki & Hari)

Sound modifies tactile sensations

→ Enhanced high frequency feedback
makes the skin feel drier
→ temporal coincidence required

  • Deprivation of one modality can modify the
    development and integration of remaining
    modalities
21
Q

parchment-skin illusion in blind people

A
  • Less susceptible to the illusion – ability to
    ignore irrelevant auditory input in the
    tactile task
22
Q

Modality appropriateness account:

A

Interference by a task-irrelevant modality is
reduced when processing accuracy of the
task-relevant modality (i.e., touch) is high
(i.e., perception is dominated by the
modality that provides the most reliable
information)

23
Q

parchment skin illusion: (vision, audition and touch)

A
  • Robust illusion in sighed humans
  • 7 of the early blind participants were
    not/ minimally susceptible to the
    illusion
  • Only 3 of the early blind participants
    showed small effects in the expected
    direction
  • Multisensory perception might not be
    innate but is – at least to some extent -
    based on experiences during early
    development → following visual
    deprivation extensive cross-modal
    changes occur (re-organisation of
    perceptual system)

note: study tested both early vs late blind subjects- only results for early shown/discussed here

24
Q

Cross-modal Plasticity in the Cerebral Cortex I

A

Study by Hamilton et al., 2000 (NeuroReport)

  • Case of blind woman who lost ability to
    read Braille following bilateral occipital
    lesions (usually processing vision) following
    stroke
  • Occipital cortex involved in decoding
    spatial and tactile information for Braille
    reading
  • Suggests that there may be a critical period of susceptibility for the recruitment of the
    occipital cortex for haptic information processing (in congenitally blind)
25
Q

Cross-modal Plasticity after Sensory Deprivation: Summary: Reorganisation in areas associated with the deprived modality

A
  • Primary sensory areas are able to process
    information from remaining modalities
  • Sensory inputs shape the functional
    architecture of the brain
  • Reorganisation likely to be limited to
    early-onset (sensitive period)
  • Caution:
    Difficulty to clearly distinct between
    primary brain areas and neighbouring
    areas (usually multi-modal) – small
    spatial resolution of TMS, PET and MRI
25
Q

Cross-modal Plasticity in the Cerebral Cortex II

A

MS – Study

Cohen et al., (1997), Nature, 389

  • TMS briefly disrupts the electric activation
    patterns of the neurons in the cortical area it is applied to
  • Blind Braille readers and sighted participants who had to identify embossed Roman letters
  • Occipital stimulation (visual area) disrupted
    Braille reading in blind participants but not
    tactile discrimination in sighted participants
    (but disrupted their visual performance)
  • Visual cortex recruited for somatosensory
    processing in early blind
26
Q

Cross-modal Plasticity after Sensory Deprivation: Summary: Reorganisation of multi-modal areas in the cortex:

A
  • Behavioural compensation for missing
    modality is mediated by enhanced
    recruitment of multi-modal areas
  • Reorganisation in multi-modal areas
    also for late-onset deprivations
  • Example: Enhanced recruitment of
    posterior STS (area of multi-modal
    integration) in deaf individuals when
    attending to moving visual displays
27
Q
A
28
Q

Interim Summary II

A
  • Cross-modal illusions, such as the parchment skin illusion, can be explained by the modality appropriateness account
  • Cross-modal perception are likely shaped by our experiences (in early development)
  • Cross-modal plasticity: Sensory deprivation in one modality affects the development/processing of the remaining modalities → reorganisation of cortical functions
29
Q

what is critical for our survival and part of human conscious experience ?

A

Perceptual distinction between one’s own body and the environment is critical for our survival and part of human conscious experience

29
Q

what does body ownership include of?

A

Body Ownership includes feeling the skin stretching around joints and digits, feeling the coolness/ warmness on the skin, feeling the tension from muscles and tendons etc. (all combined)

29
Q

state- Sense of Body Ownership is multisensory in nature (cannot be
reduced to a single modality) – not really a “sense” but a complex/multisensory perception

A
29
Q

research-

A

Research interest in experimental studies of body ownership started about 25 years ago with the description of the famous “Rubber Hand Illusion” (Botvinick & Cohen, 1998, Nature) → 3-way interaction between vision, touch & proprioception

30
Q

rubber hand illusion: how (objectively) quantified?

A
  • Questionnaires and Rating scales
  • Proprioceptive Drift (reported hand
    location changes)
  • Physiological responses (skin conductance) in response to perceived threat to the rubber hand
31
Q

perceptual rules of body ownership:

A

1.Temporal synchrony: if visual and tactile
stimulation are mismatched illusion
disappears (~ 300-500 ms)

  1. Spatial rules: e.g., distance between real
    hand and rubber hand (peri-personal
    space as constraint), identical direction of
    visual and tactile strokes, matching
    orientation & postures of hands
32
Q

what are perceptual rules similar to?

A

Perceptual Rules are similar to principles of multisensory integration

33
Q

what is sense of body ownership governed by?

A

Sense of body ownership is governed by the same principles as multisensory perception

→ multisensory integration is the key mechanism in perceiving body ownership

34
Q

Definition: Peripersonal Space

A

Space immediately surrounding our bodies in which objects can be grasped and manipulated [Space beyond grasping distance = extrapersonal space]

  • illusion strength decreases at distances > ~30 cm (peripersonal space)
35
Q

rubber hand illusion - more rules

A

-tactile congruence rule
- humanoid shape rule

36
Q

tactile congruence rule

A

Tools that touch real and rubber hand must be similar in texture and geometric features (subtle incongruences possible)

37
Q

humanoid shape rule

A

Rubber hand must resemble a human hand in shape and structure (colour and material less critical) → e.g., ownership observed for
realistic prosthetic hands or even images
of human hands

38
Q

state- Congruent pattern of multi-sensory signals drive the perceptual phenomenon!

A
39
Q

Multisensory integration of body signals

A
  • Cortex areas specifically dedicated to
    multisensory integration of body related
    signals in peripersonal space
  • Meta-analysis: areas in ventral premotor
    cortex and intraparietal sulcus that respond
    with greater activation for combined/ congruent visuotactile stimulation than for
    unimodal visual or haptic stimulation or
    incongruent stimulation
  • Generally, body ownership is associated with
    activation in multisensory areas in frontal
    and parietal lobes
40
Q

Recent studies on limb ownership:

A

Consistent activation in area EBA
of the ventral stream

41
Q

Full-Body Ownership

A
  • Illusion adheres to the same
    perceptual rules as the RH-illusion
  • Illusion seems to relate to similar
    activation of brain patters as the
    RH-Illusion (increased activity in
    ventral premotor cortex,
    intraparietal cortex and LOC)
  • Activation in ventral premotor
    cortex correlates with the strength
    of the illusion
  • Note: Entire body is perceived as one’s own (not just the stimulated parts) → requires multisensory perceptual binding
41
Q
A
41
Q

Multisensory Integration: Neuroimaging

A
  • Manipulation of temporal congruency (synchrony) and spatial congruency (hand orientation)
  • Largest activation when stimulation was both spatially and temporally congruent
  • Activation in intraparietal cortex is additive
  • Response in the pre-motor cortex is superadditive
42
Q

Individual Differences-
Something to consider

A
  • Degree of illusory experience varies
    (+about 30% of population are immune to
    the induction of the RH-Illusion)
  • Factors influencing individual differences
    are largely unknown
  • Multi-sensory account predicts that
    immunity should relate to how visual,
    tactile and proprioceptive information is
    weighted by the brain
  • People that rely more on proprioceptive
    information (e.g., dancers, gymnasts etc.)
    maybe more resistant to the illusion
42
Q

potential clinical applications- projection of ownership to advanced hand prostheses:

A

Indication that synchronised
brushing of participant’s stump and the fingers of a prosthetic hand produces RH-Illusion in some (~ 30%) amputees

42
Q

potential clinical applications- Projection of ownership to simulated bodies in VR:

A

People can maintain ownership of a virtual
hand as long as its movements are temporally
and spatially congruent with movements of real hand (allow paralysed people to “own a virtual limb” in virtual and mixed reality applications)

43
Q

final summary

A

*Rubber hand illusion and full body ownership illusions obey the
temporal, spatial and other congruency rules related to properties of the stimulus – mirroring the congruency principles of multisensory integration

  • Illusory changes in body ownership don’t depend on a single modality but reflect an (flexible) integration process of different modalities
  • Sense of body ownership is associated with increases in activity in multisensory cortical areas (e.g., premotor cortex and PPC)
  • Sense of body ownership critically depends on multisensory integration

perception- year 3 (6 decks)

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