Adaptation IV

Question 1

What is the modular approach to sensory processing?

Answer 1

There have been findings suggesting the presence of separate cortical area specialised for different sensory input processing.

Placing these cues in conflict with each other suggests that perception is actually shaped by interactions between different sensory modalities.

Question 2

What is spatial ventriloquism?

Answer 2

When a visual and auditory stimulus are presented at the same time at different locations, the auditory stimulus is shifted towards the visual location.

Ventriloquist effect typically asymmetric - perceived auditory location shift stowards the visual location but this is largely unaffected in turn.

Question 3

What is the modality appropriateness hypothesis? (Welch and Warren 1980)

Answer 3

differences in sensory estimates resolved in favour of modality most appropriate for given task.

visuo spatial acuity much better than auditory spatial acuity, so vision captures spatial location of auditory stimuli.

auditory temporal acuity > visual spatial acuity so audition captures visual stimuli in time.

Question 3

What is temporal ventriloquism?

Answer 3

Compared to spatial ventriloquism, this is in the opposite direction.

Perceived timing of visual stimuli biased towards asynchronously presented auditory stimuli. Visual stimuli have little effect on the perceived timing of auditory stimuli.

Shipley (1964) reported illusory changes in perceived rate.

Question 4

What is the maximum likelihood estimation (Ernst and Banks 2002) ?

Answer 4

this provides a mathematical representation of understanding integration of sensory cues.
it proposes that brain forms weighted average of estimates obtained from each sensory modality.

large weight assigned to estimates with low uncertainty (high sensitivity) whereas low weight given to estimates with high uncertainty.

this approach successfully considers patterns of multisensory integration in different contexts.

Question 5

What are some benefits of multisensory integration?

Answer 5

combining cues from multi sensory inputs in different modalities confers two benefits:

• resolves discrepancies associated with neural and environmental noise, helping to maintain unified percept of world.
• increases precision of perceptual judgements.

Question 6

What if it goes wrong?

Answer 6

when cues relating to differnet sources are integrated, this isnt beneficial and could be hazardous.

instead, separate estimates shoud be formed based on each sensory modality. how can the brain integrate and separate?

Question 7

What are the benefits and costs of MSI?

Answer 7

integration restricted to multisensory signals that occur close together in space and time. degree of integration shown by amount of weight given to visual stimulus e.g. 0 indicates no integration, whereas 1 indicates complete visual capture.

Question 8

Define multisensory recalibration

Answer 8

Brainard and Knudsen (1998) observed this in juvenile barn owls: they put prism goggles on them to laterally shift the visual image, causing the auditory receptive fields to laterally shift to counteract the introduced audio-visual discrepancy.

Question 9

Can multisensory recalibration occur over shorter adaptation timescales?

Answer 9

following exposure to sequential audio visaul stimuli with a consistent spatial offset, the perceived locations of auditory stimuli are shifted in the direction of conflict.

this effect can be elicited with as little as one presentation of the discrepant stimulus = brain constantly recalibrating auditory and visual positions? (Recanzone 1998)

Question 10

Define temporal recalibration

Answer 10

Repeated exposure to audio visual stimuli pairs with a consistent lag changes perceived timing of following stimuli (Fujisaki et al 2004; Vroomen et al 2004).

Question 11

What are the mechanisms of temporal recalibration?

Answer 11

Navarra et al., (2009): perceptual latency account: asynchrony adaptation changes speed of sound processing and reaction times to auditory stimuli increase to counteract visual lead and slow down to counteract auditory lead.

Question 12

How can stimulus onset asynchronies be tested to give us more information?

Answer 12

Effects of asynchrony adaptation on perception of wide range of SOAs tested - found that changes in perceived timing varied as a function of difference between adapted and tested SOAs.

Question 13

What is the population coding account of temporal recalibration?

Answer 13

Same type of explanation used for tilt and direction aftereffects, suggesting that multisensory timing might be processed in analogous manner to simple unisensory items.

Results consistent with model of audio visual timing represented by neurons tuned to different SOAs.

Question 14

What is the implication of the superior colliculus in multisensory integration?

Answer 14

MSI has been thoroughly studied in SC, as it receives input from ascending visual, auditory and somatosensory pathways and descending cortical projections.

Cells in superficial layers are visual, but deep layer cells often bimodal: e.g. audiovisual or visual-somatosensory) and sometimes trimodal (AVS)

Question 15

What is super-additivity in the SC?

Answer 15

The response to bimodal/trimodal input being greater than the sum of unimodal responses. Studies of multisensory integration in SC have found three rules:
1. Spatial rule (maximum response achieved with co-located stimuli)
2. Temporal rule (inputs approximately aligned in time)
3. Inverse effectiveness rule (superadditivity strongest when responses to modality specific input is weak (Meredith and Stein 1986)

Question 16

How has the association cortex been implicated in MSI?

Answer 16

In the cerebral cortex, a few associated areas have been found that receive converging inputs from multiple sensory mediums, in particular:

posterior portions of STS
regions of posterior parietal cortex, i.e. lateral and ventral intraparietal areas (LIP, VIP) (Bremmer 2011)

Question 17

How has the primary sensory cortex been implicated in MSI?

Answer 17

research evidence challenged modular view e.g. direct anatomical connections between V1 and A1 found (Falchier et al. 2002), fMRI imaging suggesting activation of auditory cortex during silent lipreading (Calvert et al., 1997) and cross modal recruitment of occipital visual cortex in blind and auditory cortex in the deaf (Merabet and Pascual Leone 2010)