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If attention moves in quantal jumps how can the mouse get his cheese?

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... of the second target locations fall on the circumference of an invisible circle, ... Most theories of visual perception assume a pre-attentive stage that initially ... – PowerPoint PPT presentation

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Title: If attention moves in quantal jumps how can the mouse get his cheese?


1
If attention moves in quantal jumps how can the
mouse get his cheese?
  • David Crundall
  • Rm 315

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If attention jumps from one place to another,
rather than moves in an analogue fashion, then
how do we perform this task? Jolicoeur et al.
(1986, 1991) tested participants abilities to
perform a simplified version of this task. Two
convoluted lines were presented with one of them
passing through the point of fixation. The task
was to say whether two targets fell on the same
line or fell on different lines. The first target
was always presented at the point of fixation.
5
A typical stimulus used in Jolicoeurs studies
All of the second target locations fall on the
circumference of an invisible circle, ensuring
that all second targets are the same distance
from the first target in Euclidean space.
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The line tracer slows down for hair-pin bends
(Jolicoeur, Ullman Mackay, 1991)
9
The proximity of distracter lines affects how
fast the line tracer can travel
(Jolicoeur, Ullman Mackay, 1991)
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The line-tracing process appears to be automatic
11
Results for response times to targets on the same
curve
Pringle and Egeth (1988)
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  • To summarise
  • There appears to be a serial analogue movement of
    attention that traces lines.
  • It is sensitive to curvature
  • It is affected by the proximity of distracter
    curves
  • It appears to be automatic rather than under
    strategic control

14
Scholte, Spekreijse Roeflsema (2001)
  • Does attention parse all curves pre-attentively?
  • Or does attention strategically jump along the
    line to points of ambiguity (i.e. can a quantal
    movement of attention still account for line
    tracing)?
  • Or does attention just trace the target line?

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Findings from Scholte et al (2001)
  • The lines are not pre-attentively parsed, as the
    crossovers should not increase RTs and colours
    should be reported equally as well from both
    lines.
  • Attention traces the whole line and does not jump
    from one point to another, otherwise the colours
    on the target line should have been reported as
    poorly as those on the distracter line.
  • There is leakage when lines cross, with attention
    leaking into the distracter line.
  • Conclusion? Is it an analogue movement of
    attention, or is it something else entirely,
    related to object-based perception

17
Does the line tracing operator have a real role
to play in parsing objects?
Most theories of visual perception assume a
pre-attentive stage that initially parses a scene
into candidate objects or proto-objects on the
basic of Gestalt groupings of features (Bayliss,
1998 Rensink, 2000) Curvature and collinearity
can be processed in parallel (Fahrl, 1991 Field,
Hayes, Hess, 1993) The line tracing operator
is therefore too slow to provide any valuable
input into the processing of natural
scenes (Boucart, Delord, Giersch,1994)
18
But...
  • Gestalt grouping does not occur if attention is
    directed else where
  • (Ben-Av, Sagi, Braun, 1992)
  • Some researchers now suggest that attention needs
    to spread across a visual scene to segregate
    objects
  • (Roelfsema, Lamme, Spekreijse, 2000)
  • Scholte et al. (2001) have suggested that there
    are in fact two levels of object parsing
  • Base grouping
  • Incremental grouping a spread of attention
    through the line rather than an analogue movement

19
Houtkamp, Spekreijse, Roelfsema (2003) did the
same experiment but the colours appeared at
varying SOAs after the lines appeared.
20
So is line tracing really object parsing?
Attention doesnt move like an analogue spotlight
but spreads through the object instead.
21
Or does it? Houtkamp et al.s secondary task may
have led subjects to adopt certain strategies
that favoured reporting the colours. Ideally we
need a single task that can distinguish between
spreading or moving attention.
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Conclusions
Attention automatically moves along a line in
order to reach a second target. Is this a
special example of analogue movement? Or is it a
spread of attention? Is line tracing used in
real life, or is it a special case that can only
be seen in the laboratory? Could it still be part
of the object parsing process?
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