Attention and Scene Perception 8 Attention and Scene Perception

The Physiological Basis of Attention Three ways responses of a cell could be changed by attention: wolfe2e-fig-08-19-0.jpg

The Physiological Basis of Attention Attention could enhance neural activity Attention to a specific part of the visual field causes neurons to code those locations to have increased activity This increased activation has been detected using fMRI technology

Figure 8.15 Spotlights of attention in the human brain wolfe2e-fig-08-15-0.jpg

The Physiological Basis of Attention Attention could enhance the processing of a specific type of stimulus Fusiform face area: An area in the fusiform gyrus of human extrastriate cortex that responds preferentially to faces in fMRI studies Parahippocampal place area: A region of cortex in the temporal lobe of humans that appears to respond strongly to images of places (as opposed to isolated objects)

fMRI reveals that different pieces of the cortex are activated by faces and by places wolfe2e-fig-08-17-0.jpg

What can go wrong: Disorders of Visual Attention Neglect: inability to attend to or respond to stimuli in the contralesional visual field Typically, neglect of the left visual field after damage to the right parietal lobe Contralesional field: The visual field on the side opposite a brain lesion For example, points to the left of fixation are contralesional to damage to the right hemisphere of the brain Ipsilesional field: The visual field on the same side as a brain lesion

Figure 8.21 Five images through the brain of a neglect patient (viewed as though from above) wolfe2e-fig-08-21-0.jpg

Figure 8.22 A neglect patient would produce this sort of result if asked to cross out all the lines on the page wolfe2e-fig-08-22-0.jpg

Figure 8.23 This is what can happen when a neglect patient tries to copy a drawing wolfe2e-fig-08-23-0.jpg

Disorders of Visual Attention Attention can be object-based Evidence from neglect patients indicates that they sometimes neglect one side of an object rather than one side of the visual field Tipper and Behrmann’s (1996) experiment

Disorders of Visual Attention Extinction: In visual attention, the inability to perceive a stimulus to one side of the point of fixation (e.g., to the right) in the presence of another stimulus, typically in a comparable position in the other visual field (e.g., on the left side) Balint syndrome: Results from bilateral lesions of the parietal lobes Spatial localization abilities are greatly reduced Balint syndrome patients don’t move their eyes very much Balint syndrome patients have simultagnosia: An inability to perceive more than one object at a time

Perceiving and Understanding Scenes What does it mean to see more than one object? How do we perceive entire visual scenes?

Figure 8.25 Spend a second or two looking at each of these pictures wolfe2e-fig-08-25-0.jpg

Perceiving and Understanding Scenes Now look at this second version of the figure and see if you can tell what has changed...

Figure 8.26 Which of these pictures did you see in Figure 8.25? wolfe2e-fig-08-26-0.jpg

Figure 8. 26 Which of these pictures did you see in Figure 8. 25 Figure 8.26 Which of these pictures did you see in Figure 8.25? (Answer key) wolfe2e-fig-08-26-0.jpg

Perceiving and Understanding Scenes Change blindness: The failure to notice a change between two scenes If the change does not alter the gist, or meaning, of the scene, quite large changes can pass unnoticed Demonstrates that we don’t encode and remember as much of the world as we might think we do

Perceiving and Understanding Scenes Local and global approaches to scene recognition Local approach: Identify the individual objects in a scene and use the identities of the objects to determine what the scene is Global approach: Identify the entire scene all at once, without identifying individual objects within it

Perceiving and Understanding Scenes Local approach to scene recognition: Scene recognition can happen very quickly How might we quickly identify objects in a scene without having to look at each one? Covert attentional shift: A shift of attention in the absence of corresponding movement of the eyes

Perceiving and Understanding Scenes Global approach to scene recognition Perhaps it is not necessary to recognize individual objects in order to recognize a scene Spatial layout: The description of the structure of a scene without reference to the identity of specific objects in the scene Open, enclosed, rough, smooth, natural, artificial, etc.

Figure 8.31 Spatial layout from global information wolfe2e-fig-08-31-0.jpg