HUL 211 Attention as a control mechanism

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HUL 211 Attention as a control mechanism Powered By Docstoc
					Attention as a control mechanism

          Snehlata Jaswal

Attention is the mechanism which implements the dictates of the
top executive. It is essentially a selective mechanism that allows
processing of only a few stimuli from among the multitude which
the world comprises.

Attention is the cognitive process of selective allocation of
processing resources

Attention has a limited capacity and operates like a bottleneck in
the information processing sequence

                      HUL 211 OBJECT PERCEPTION AND MEMORY
           Attention is a bottle neck
“Cocktail party problem“ Cherry (1953)

Dichotic listening experiments : Subjects would use a set of headphones to listen
to two streams of words in different ears and selectively attend to one stream.
After the task, the experimenter would question the subjects about the content of
the unattended stream. Subjects could not extract meaning from the unattended
stream, giving rise to the idea that attention has a limited capacity.

But Treisman pointed out that subjects could respond to some stimuli such as
their names even in the unattended ear.

This debate became known as the early-selection vs late-selection models. In the
early selection models attention shuts down or attenuates processing in the
unattended ear before the mind can analyze its semantic content. In the late
selection models the content in both ears is analyzed semantically, but the words
in the unattended ear cannot access consciousness.This debate has still not
been resolved.

                          HUL 211 OBJECT PERCEPTION AND MEMORY
                Types of Attention
Attention is classified in many ways:

James (1890) and Wundt (1897)
       Voluntary attention
       Involuntary attention

Posner (1980): Endogenous and exogenous attention

Spatial attention
Object based
Feature based

                      HUL 211 OBJECT PERCEPTION AND MEMORY
                 Types of attention
ENDOGENOUS                                 EXOGENOUS
Top down                                   Bottom up
Voluntary                                  Involuntary
Effortful                                  Automatic
Slow to develop (in about 200-300          Rapid (develops within 100 ms)
Sustained over a period of time            Transient
Functions by perceptual                    Functions by affecting the
enhancement of the stimulus                tendency to respond, irrelevant
focused on                                 cues capturing attention away
                                           from the motor response
Entirely cortical neurons involved         Cortical as well as sub cortical
                                           neurons are involved
                       HUL 211 OBJECT PERCEPTION AND MEMORY
                  Spatial attention
Spatial attention implies attention to locations

It is thought to operate as a two-stage process

1st stage:
        Parallel processing
        Attention is distributed uniformly over the visual scene

2nd stage:
        Serial processing
        Attention is focused on a specific area of the visual scene

                       HUL 211 OBJECT PERCEPTION AND MEMORY
          Spatial attention - models
Spotlight model (LaBerge 1983, after James, 1890): Attention has a focus,
a fringe, and a margin. The focus extracts information from the visual
scene with a high-resolution, the geometric center of which is where
visual attention is directed. Surrounding the focus is the fringe of
attention which extracts information in a much more crude fashion (i.e.
low-resolution). The fringe extends out to a specified area and this cut-off
is the margin.

Zoom-lens model (Eriksen and St. James, 1983) This model inherits all
properties of the spotlight model (i.e. the focus, the fringe, and the
margin) but has the added property of changing in size. This size-change
mechanism was inspired by the zoom lens of a camera, and any change in
size can be described by a trade-off in the efficiency of processing. Since
attentional resources are fixed, the larger the focus, the worse or slower
the processing of that region

                         HUL 211 OBJECT PERCEPTION AND MEMORY
                Object based attention
Duncan (1996, 1998, 2006) holds that as attention is focussed on an
object, all features of the object are strengthened. In his model,
attention is an emergent entity that accompanies the identification
and further processing of objects.

When a cued object moves to a new location, attention moves with
the object, rather than being tied to the same location (Kahneman,
Treisman, and Gibbs, 1992).

It is possible to identify targets appearing within a cued object faster
than an uncued object (Moore, Yantis, & Vaughan, 1998).

It takes longer to move the focus of attention a particular distance
between two different objects than it does to traverse the same
distance if it is within an object (Egly, Driver & Rafal, 1994).
                        HUL 211 OBJECT PERCEPTION AND MEMORY
    Egly, Driver and Rafal (1994)

Egly, Driver & Rafal (1994) found that it
takes longer to move the focus of
attention a particular distance between
two different objects than it does to
traverse the same distance if it is within
an object

                    HUL 211 OBJECT PERCEPTION AND MEMORY
      Spatial vs. object based attention
Using eye tracking, Becker and Rasmussen (2008) have shown with
real world scenes that attention is first directed to locations and
then to objects, and both are guided by familiarity coded in LTM for

Shomstein and Behrmann (2008) have shown that object based
effects show up better at longer exposure durations (1000 ms) than
at shorter exposure durations (200 ms). Crucially, they also found
that whereas 200 ms preview time is sufficient for object
configuration to guide target detection, it is not powerful enough to
show its effect in a more difficult target discrimination search task.

It seems that attention to locations precedes attention to objects.

                      HUL 211 OBJECT PERCEPTION AND MEMORY
                  Feature based attention
In a priming paradigm, visual search is facilitated if the target shares features
with the preceding target (Kristjansson, 2006).

Feature based attention facilitates the guidance of attention to a target object
only when location information is unavailable (Moore & Egeth, 1998, Shih &
Sperling, 1996).

Neurophysiological evidence suggests that spatial and feature based attention
may not function additively (McMains, Fehd, Emmanouil, & Kastner, 2007).

Zhang and Luck (2009) have recently demonstrated that feature (colour) based
attention can affect feed forward processing within 100 ms of stimulus onset,
even for stimuli presented at an unattended location. The only condition for
this effect seems to be that the stimuli must be presented simultaneously, i.e.,
under conditions of competition. Sequential presentation destroyed the effect.
Spatial attention still remains special because it alone affects early processing
even in the absence of competition.
                            HUL 211 OBJECT PERCEPTION AND MEMORY
      Object × Feature × Spatial attention
It is easier to identify two features within a single object as
compared with two features in two different objects:

- even if the two different objects were superimposed on each
other in the same location (Awh, Dhaliwal, Christensen, &
Matsukura, 2001; Duncan, 1984; Lee & Chun, 2001; Vecera,
1997; Vecera & Farah, 1994)

 - even when one object is partially occluded by another object
(Behrmann, Zemel, & Mozer, 1998)

 - even when spatial cues are used to direct attention to a part of
the display (Law & Abrams, 2002).

                        HUL 211 OBJECT PERCEPTION AND MEMORY
                      Attention in binding
The role of attention in binding was first emphasized by Treisman and Gelade
(1980) who postulated that attention is the glue that binds features together.

Hyun, Woodman, and Luck (2009) used the N2pc component of ERPs as a
measure of attention. They observed a larger N2pc component in the binding
condition in comparison to a feature detection condition.

Fougnie and Marois (2009), who found that memory for colour-shape binding,
was more disrupted than the memory for single features when an attention
demanding multiple object tracking task was given during the retention interval.

On the other hand, some researchers have found that the same amount of
attention is required for detection of features as for binding them together (Allen
Baddeley, & Hitch, 2006; Johnson, Hollingworth, & Luck 2008; Joseph, Chun, &
Nakayama, 1997; Kim & Cave, 1995; Theeuwes, Van der Burg, & Belopolsky,
2008) while others contend that bindings can be detected and maintained
without attention (Eckstein, 1998; Gajewski & Brockmole, 2006; Mordkoff &
Halterman, 2008; Palmer, Verghese, & Pavel, 2000).
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              Functions of attention
Enhancement of the object focussed on

Suppression of the surround

Sharpening the response

Attentional protection

Attention in task switching

Multitasking - dividing attention


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                  Methods of study
Experimental instructions – Incidental vs. intentional learning



After cues

Distractors – Attention capture

Dual task method – Dichotic listening, Inserting a task between study
and test

Recording physiological measures – ERPs, fMRI etc.

                       HUL 211 OBJECT PERCEPTION AND MEMORY
         Thank you


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