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HUL 211 Location in object perception and memory

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HUL 211 Location in object perception and memory Powered By Docstoc
					The role of location in object
  perception and memory




        Snehlata Jaswal


         HUL 211 OBJECT PERCEPTION AND MEMORY
                 Location as a feature
Location is one of the features of an object

Processing locations in perception:

Processed in a different stream (dorsal stream)
Processed much faster
Greater automaticity in processing

Processing locations in memory:

Courtney, Ungerleider, Keil, and Haxby (1996) using PET found
differential patterns of activation in the prefrontal cortex associated with
memory for location and memory for object identity.

Xu and Chun (2006) found that whereas memory for identity of objects
recruited the superior intraparietal sulcus and the lateral occipital
complex, memory for locations involved the inferior intraparietal sulcus.

                          HUL 211 OBJECT PERCEPTION AND MEMORY
      Location as a special feature?
Feature integration theory
(Treisman and Gelade, 1980, Treisman and Sato, 1990)

In contrast to other stimulus properties, location plays a key
role in binding.

While basic visual features are detected relatively
automatically and are processed in parallel, participants
cannot know which of these features go together unless
attention is focused on particular locations.

Focusing attention on a particular spatial location allows the
features at that location to be bound together so that an item
can be identified

                     HUL 211 OBJECT PERCEPTION AND MEMORY
       Location as a special feature?
Guided Search model (Wolfe, Cave, and Franzel, 1989; Wolfe, 1994)
The guided search model proposed that the features processed in the
parallel stage guided attention in the subsequent serial stage, primarily by
dividing the stimuli into distracters and probable targets.

Further, it provided evidence that search for conjunctions defined by three
features was more efficient than conjunctions of two features, simply
because more number of features guided search for triple conjunctions.

Wolfe (1994) acknowledged the special role of location by modifying the
model to suggest that the output of processing in the initial massively
parallel stage guided spatial attention and thus the second serial stage
processed input from a limited portion of the visual field.

This reverses the sequence of the relative influence of location and other
features postulated by the feature integration theory, which holds that other
features are attached to a master map of locations and hence spatial
attention precedes and guides attention to features (Treisman & Sato,
1990).                    HUL 211 OBJECT PERCEPTION AND MEMORY
        Location in object perception
Keele, Cohen, Ivry, Liotti, and Yee (1988) found that there is no tendency for
synchronicity of features to cause binding unless they came from the same
location, and thus concluded that location rather than temporal synchronicity is the
essential cue for binding.
Fahle and Koch (1995) used the ambiguous figure of the Kanizsa triangle to test
whether the dominant percept is determined by spatial alignment or simultaneity of
presentation of all elements. Spatial displacement destroyed figural binding, but
even major temporal asynchronies had no effect on figural binding.
Wheeler and Treisman (2002) found that participants were better at remembering
locations than colours. They obtained ceiling effects for the memory for locations,
which also did not show any decrease as the number of stimuli increased from 3 to
6, thus substantiating their assumption that location is a special feature of
multidimensional stimulus representations.
Treisman and Zhang (2006) randomized location to control its effect when the
binding of shape and colour was tested, to find that binding is more dependent on
location than single features, and more so at 100 ms than at longer study-test
intervals.
Mitroff and Alvarez (2007) reported that contiguity in space and time rather than
surface features, guides the persistence of objects, even if the object disappears
for as long as 3 seconds.

                           HUL 211 OBJECT PERCEPTION AND MEMORY
Kanisza triangle




 HUL 211 OBJECT PERCEPTION AND MEMORY
          Location in object memory
Phillips (1974) performance was better at short durations when test arrays were
presented at the same location as the sample array, suggesting a retinotopic
memory store. But, at inter-pattern intervals of 300 ms or greater, changes in the
retinal location of test arrays had little effect on accuracy.
Irwin (1991) used 4×4 arrays of dots as the experimental stimuli, and found that
displacement of the second pattern disrupted performance at 1 and at 70 ms, but
had no effect at 600 and 5000 ms

Jiang, Olson, and Chun (2000) using a change detection task with the probe
display presented 907 ms after the study display, reported that detection of
changes in single items was reduced when the spatial configuration of array
elements was changed. They concluded that though memory for the absolute
location of single items is not important, the global configuration is important, and
relational processing does take place for items in VWM
Wheeler and Treisman (2002) found that participants were better at remembering
locations than colours. They obtained ceiling effects for the memory for locations,
which also did not show any decrease as the number of stimuli increased from 3 to
6, thus substantiating their assumption that location is a special feature of
multidimensional stimulus representations.


                           HUL 211 OBJECT PERCEPTION AND MEMORY
          Location in object memory
Using real objects as stimuli in a change detection task with 900 ms between the
study and the probe display, Hollingworth (2007) reported better performance when
the object remained in the exact same position. However, if all the other objects
changed their relative spatial relationships, this same position advantage for the
target was lost, indicating that the map of the visual space as a whole is a critical
factor in the memory for objects even at 900 ms.

The importance of location for bindings in VSTM has been established not only for
objects placed in a two-dimensional single plane, but also when they are placed in
3-D surfaces. A greater number of objects could be held in VSTM when they were
placed in two different 3D surfaces (either vertical or horizontal) than in a single
plane. This advantage was evident, however, only when participants had to bind
which colour appeared where. When the colour-location binding was not required,
and participants were to remember only colours, no benefit accrued from the extra
spatial dimension. In other words, the extra dimension, being germane to locations,
was important for the response only when locations were a relevant feature in the
memory of bindings (Xu & Nakayama, 2007).

Conclusion: VWM is not influenced by absolute location of items except when
location is bound with other features as in real objects or is relevant to task
performance. .
                           HUL 211 OBJECT PERCEPTION AND MEMORY
         Thank you




HUL 211 OBJECT PERCEPTION AND MEMORY

				
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posted:5/7/2012
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Description: Object Perception and Memory Lecture Series