Attention to space and objects

Space-based attention

Spotlight analogy

• Hermann von Helmholtz (1894)
• Centrally fixed gaze
• Part of screen illuminated by electric spark
• Individual could discern letter if attention was directed towards that region prior to the spark
• First demonstration of covert attention - a shift of attention without moving the eyes or head

Zoom lens theory

• Modification of spotlight approach
• area of focal attention can be adjusted in line with task demands
• Spatial attention may not be restricted to a single circular area
• The focus of attention can also move instantaneously from one location to another without a cost for the amount of distance travelled
• Visual spatial atetention is clearly more flexible than the spotlight or zoom lens models would predict. However, the general concept of 'space-based attention' is still fundamental

Evidence for space-based attention from studies of disorders of attention

• damage to the right hemisphere - especially within the parietal lobe - often leads to symptoms of the neglect syndrome 
• Patients fail to acknowledge that objects or events exist in the hemispace opposite to their lesion
• Neglect for the left side of space is more common than neglect of the right side of space. This is likely because the right hemisphere represents left and right space, whereas the left hemisphere tends to represent right space alone (Mesulam, 1999)

Spatial neglect

- Neglect patients tested on Posner's cueing tasks have difficulty orienting attention to the neglected side

- Neglect patients have particularly difficulty disengaging attention

- Neglect patients with Parietal damage only can still process illusory figures that are connected by subjective contours, suggesting that the grouping features in the neglected visual field may occur despite apparent spatial neglect

Visual Extinction - similar to visual neglect; it is the failure to consciously perceieve of respond to a stimulus that is on the opposite side of the lesion when presented simultaneously with a stimulus that is on the same side as the lesion

Pseudoneglect in neurotypical individuals

- In a non-lesioned brain there is an attentional bias for the left side of space

 

Object-based attention

• Attention is directed not only to spatial locations but also to perceptual objects
• When viewing natural scenes, eye moevements are directed almost exclusively to objects
• Attention can be directed to objects independently of regions of space
• Attention to face: activation in fusiform face area
• Attention to house: activation in parahippocampal place area
• Attention to visual motion: activation in area MT/MST

Attention prioritises objects over regions of space

- It is easier to judge two attributes belonging to one object than the same two belonging to different objects, even though the spatial distance between the two attributes is the same in both cases