Perception

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Perception Attention

• Keith Clements

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Aims

• Discuss how information about selected aspects of
  visual input is represented within the visual
  system.
• Discuss how selectively attending to stimuli
  alters the brain electrical activity associated
  with those stimuli.
• Discuss the relationship between brain activity
  and subjective awareness, fMRI mindreading and
  the binding problem.

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Perception and the nervous system

• Transduction
• Coding
• Topographical organisation

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viperlib.york.ac.uk
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Receptive fields in the retina, visual pathways
and visual cortex

• Kuffler (1953) recorded from neurons in the
  retina. Hubel Weisel, (1958, 1963) recorded
  from higher levels in the visual system.
• Retinal receptive fields are circular.
• Cells in visual cortex had oblong structure and
  were sensitive to elongated areas of light.
• Cells were selectively responsive to lines of
  particular orientation.

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viperlib.york.ac.uk
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viperlib.york.ac.uk
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Attention neural activity

• Moran Desimone (1985)
• Showed that attention alters the response of
  visual neurons to stimuli. The response to
  non-attended stimuli is attenuated.
• Recorded from cells in area V4 with large
  receptive fields
• Two stimuli presented simultaneously. Prior
  testing showed that one would effectively excite
  the cell, the other was less effective (based on
  colour, orientation, etc.).
• Monkeys were required to attend to one stimulus
  and ignore the other

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Fixation Point
Receptive Field
Attending to the cells preferred stimulus
produced increased activity, attending to the
non-preferred stimulus produced a response around
half as large
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ERPs and attention

• ERP components, may be defined as
• Bumps troughs in the signal
• Task-sensitive aspects of the signal
• Presumed neural generators
• Exogenous components
• Obligatory, stimulus-driven
• Endogenous
• Optional related to processing

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From Curtin, URL www.sprweb.org/teaching/index.htm
lLectureMaterials
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Exogenous components attention

• N1 attentional filtering
• Hilyard et al. (1973) showed that the auditory N1
  component was enhanced by attention to stimuli.
• ERPs cannot localise the source of a signal, but
  MEG places the generator in the area containing
  the auditory cortex.
• Divided attention reduces the amplitude of N1
  (Wickens, Kramer, Vanasse, and Donchin, 1983)
• Visual N1 is also enhanced by attention in cuing
  studies.

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Endogenous components

• P300
• Identified by Sutton et al. (1965), they claimed
  it reflected information delivery
• Elicited by infrequent, complex and significant
  stimuli
• Typically studied in the oddball paradigm.
• Is also enhanced by attention, and typically only
  appears for attended stimuli (Pritchard, 1981).
• Also reduced by divided attention (Isreal et al.
  1980)
• Donchin (1981) context updating?
• But is not a single wave, Frontal P3a, Parietal
  P3b

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From Curtin, URL www.sprweb.org/teaching/index.ht
mlLectureMaterials
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fMRI Mindreading

• Kamitani Tong (2005)
• Used fMRI to record responses of areas of early
  visual cortex to eight gratings of different
  orientations. Activity divided into 400 voxels
  (3x3x3mm). Used information to produce weighted
  averages for each participant (n4) which could
  predict orientation.
• Could predict what grating participants were
  looking at. Prediction was still good when tested
  31 40 days after training.
• With overlapping gratings could detect which of
  two orientations participants were attending to.

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Haynes Rees

• Using a similar process were able to detect the
  orientation of masked stimuli.
• Gratings presented briefly with masking stimuli
  to prevent awareness still gave rise to
  predictable patterns of activity.
• Changes in activity paralleled the switches in
  perception when different gratings were presented
  to each eye.

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http//www.cbs.mpg.de/MPI_Base/NEU/Calendar/2006/0
2/28_1800_WilhelmWundtRaum_/haynes.pdf
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The binding problem

• How are separate neural representations combined?
• Engel co-workers (e.g 1992) suggested that
  neurons representing the same object fire in
  synchrony.
• Recorded from two neurons receptive fields
  sensitive to moving vertical bars.
• Moving stimuli triggered bursts of activity.

Synchronised Less synch. Unsynchronised
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Evidence for synchronization

• Engel et al review evidence that neurons which
  both respond to the same features tend to fire in
  synchrony.
• De Fries (1997) showed that when different
  gratings were presented under conditions of
  binocular rivalry, neurons sensitive to the
  orientation of the preferred eye showed enhanced
  synchronisation, neurons sensitive to the
  non-preferred showed reduced synchronisation.

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References

• ERPs Attention
• Hugdahl, K. (1995). Psychophysiology The
  Mind-Body Perspective. London Harvard University
  Press. Chapter 12
• fMRI Mindreading
• Kamitani, Y Tong, F. (2005). Decoding the
  visual and subjective contents of the human
  brain. Nature Neuroscience, 8, 679-685.
• Available from http//www.psy.vanderbilt.edu/tong
  lab/publications.html
• Haynes, JD Rees, G. (2005). Predicting the
  Stream of Consciousness from Activity in Human
  Visual Cortex. Current Biology, 15(14) 1301-1307.
• Possible limitations of fMRI
• Logothetis, N.K. (2008) What we can do and cannot
  do with fMRI. Nature, 453, 869-877.
• Yevgeniy B. Sirotin, Aniruddha Das (2009).
  Anticipatory haemodynamic signals in sensory
  cortex not predicted by local neuronal activity.
  Nature, 457, 475-479.
• The Binding problem
• Engel, AK., Fries, P. , König, P, Brecht, M.
  Singer, W. (1999).Temporal Binding, Binocular
  Rivalry, and Consciousness. Consciousness and
  Cognition 8, 128151