Object based attention

Advanced attentional processing can take place when it is based upon an object rather in the environment rather than a particular location. There is evidence for both location and object based models, seen in patients with visual neglect anad fMRI studies...

Attentional Disorders: Unilateral neglect and extinction

• Individuals suffering from unilateral neglect tend to have a lack of awareness of stimuli that are presented to the contralesional side of space (the side opposite to the damage).
• There is usually damage to the right hemisphere, particularly in the inferior parietal lobe so there is little awareness of stimuli in the left visual field.
• Driver and Veilleumier, 2001 said 'neglect patients often act as if half of their world no longer exists. In daily life, they may be oblivious to objects and people on the neglected side of the room, they may eat from only one side of their plate, etc.'
• Extinction is when an individual can detect a single stimulus that is presented to the left of the visual field, but fail to detect a similar stimulus when it is presented to the right of the first one.

Halligan & Marshall, 1994

• Two flowers were presented to a neglect patient and they were asked to draw what they see. The patient recognizes both flowers but cannot see the left hand hide of both. This implies there is attention to the object rather than the region of space.

O'Craven, Downing and Kanwisher (1999)

• Participants are presented an image with a face superimposed onto a house.
• They are asked to attend to either the face, the house or the motion.
• An fMRI was used to detect the activity in the Fusiform Face Area and the Parahippocampal Place Area. It detects the % change in signal.
• The location based model would suggest that participants should attend equally to both stimuli.
• The result show that there is greater activation in the FFA (fusiform face area) when the face is moving and PPA (parahippocampal place area) when the house is moving.
• This indicates that whole objects are selected and provides evidence that objects are units of attention selection, as the whole object is selected when only one visual attribute is relevant.
• This is a demonstration of attentional modulation of neural responses
• However... in 2000
• They focussed on a central fixation point
• They presented 2 ovals, one to the left and one to the right of the fixation point. Each oval was superimposed on a task irrelevant face or house
• The task was to indicate the orientation (left or right) of the one in a certain colour.
• fMRI showed that, based on activation findings, from 1999 study, there was greater processing of the stimulus superimposed on the attended oval than the unattended one
• This provides evidence that attention can be location based.

Models of Visual Attention

Humans have an ability to not attend to all the features of the environment. This offers a functional advantage. There is a focus as to how we direct our attention to specific details.

• An example of a location based model is the Spotlight & Zoom-Lens model
• Alternately there is an Object Based model

Spotlight of Visual attention

• This says that everything within a small region of visual field can be seen clearly. It is more difficult to see anything that doesn't fall within that beam.
• The information that is within the spotlight is processed more clearly than anything outside.
• Precueing Procedure - Posner et al. (1980). In this experiment, participants had to identify when a light appears. In the centre of the row, a precue was given to direct attention to the right or left. When a valid cue was given, there were faster reaction times than when an invalid cue was given. This supports the model of location based attention as the individuals spotlight of visual attention is diverted by the precue, making the light more easy to identify when it is within that visual field, or, more difficult to identify if it is outside the spotlight.

Zoom Lens Model

• This is an adaptation of the spotlight model.
• It says that attention is directed to a particular region of visual field.
• The area however ca be increased or decreased depending on the requirements.
• LaBerge (1983): In this experiment, participants were presented with 5 letter words. There were 2 conditions. In one condition, a probe would appear in place of a letter, in the other condition however, the probe would appear in place of a word. The results showed that the reaction time was faster when the participants had a narrower attentional beam, ie. in the first condition.
• There is less evidence for the zoom-lens than for the spotlight model, as we can still process unattended visual stimuli.