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Chapter 6: Visual Attention

Chapter 6: Visual Attention. Scanning a Scene. Visual scanning – looking from place to place Fixation Saccadic eye movement Overt attention involves looking directly at the attended object Covert attention is attention without looking. Figure 6-1 p128. Figure 6-2 p129. Figure 6-3 p129.

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Chapter 6: Visual Attention

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  1. Chapter 6: Visual Attention

  2. Scanning a Scene • Visual scanning – looking from place to place • Fixation • Saccadic eye movement • Overt attention involves looking directly at the attended object • Covert attention is attention without looking

  3. Figure 6-1 p128

  4. Figure 6-2 p129

  5. Figure 6-3 p129

  6. What Directs Our Attention? • Characteristics of the scene: • Stimulus salience - areas of stimuli that attract attention due to their properties • Color, contrast, and orientation are relevant properties. • Saliency maps show fixations are related to such properties in the initial scanning process.

  7. Figure 6-4 p130

  8. Figure 6-5 p131

  9. Selection Based on Cognitive Factors • Picture meaning and observer knowledge • Scene schema - prior knowledge about what is found in typical scenes • Fixations are influenced by this knowledge

  10. Selection Based on Cognitive Factors - continued • Experiment by Shinoda et al. • Observers’ fixations were measured during computer simulated driving. • They were more likely to detect stop signs when they were at intersections. • People have learned that this is where stop signs are typically placed.

  11. Figure 6-6 p131

  12. Task Demands • Influence of the observer’s task • Task demands override stimulus saliency. • Eye movements and fixations are closely linked to the action the person is about to take. • Dynamic environment experiment, Jovancevic-Misic and Hayhoe (2009)

  13. Figure 6-7 p132

  14. What Happens When We Attend? • Attention to specific locations is called spatial attention • Experiment by Posner (1978) et al. • Observers looked at a fixation point. • Precueing with an arrow indicated on which side a stimulus was likely to appear. • Stimuli appeared that were consistent (valid trial) or inconsistent (invalid trial) with the cue. • Task was to push button when a target square was seen.

  15. What Happens When We Attend? - continued • Results showed that observers responded fastest on valid trials. • Posner believed these results showed that information processing is most efficient where attention is directed.

  16. Figure 6-8 p133

  17. Figure 6-9 p133

  18. What Happens When We Attend? - continued • Experiment by Egly et al. • Observer views two rectangles. • Cue signals where target may appear. • Task was to press button when target appeared. • Results show: • Fastest reaction time at targeted position • “Enhancement” effect for non-target within the target rectangle

  19. Figure 6-10 p134

  20. Figure 6-11 p134

  21. Attention Can Influence Appearance • Experiment by Carrasco et al. • Observers saw two grating stimuli with either similar or different contrast between the bars. • Task was to fixate on center point between gratings and indicate orientation of bars with higher contrast. • Small dot was flashed very quickly on one side before gratings appeared.

  22. Attention Can Influence Appearance. - continued • Experiment by Carrasco et al. • Results showed that: • when there was a large difference in contrast, the dot had no effect. • when the contrast was the same, observers were more likely to report that the grating preceded by the dot had higher contrast. • Thus the shift of attention led to an effect on perception

  23. Figure 6-12 p135

  24. Attention Can Influence Physiological Responding • O’Craven (1999) – Subject attended to the house or face show that attending to the moving or stationary face caused enhanced activity in the FFA and attending to the moving or stationary house caused enhanced activity in the PPA

  25. Figure 6-13 p135

  26. Attention Can Influence Physiological Responding - continued • Datta and DeYoe (2009) • Attention maps show directing attention to a specific area of space activates a specific area of the brain. • Womelsdorf (2006) – showed that attention can cause a monkey’s receptive field to shift toward the place where the attention is directed.

  27. Figure 6-14 p136

  28. Figure 6-15 p137

  29. What Happened When We Don’t Attend? • Inattentional blindness - a stimulus is not perceived even when the person is looking directly at it • Experiment by Simons and Chabris (1999) • Observers are shown short film of teams passing a basketball. • Task is to count number of passes. • Either a woman with an umbrella or a person in gorilla suit walks through the teams. • 46% of observers fail to report the woman or gorilla.

  30. Figure 6-16 p138

  31. Figure 6-17 p138

  32. Change Detection • Change blindness • Observers were shown a picture with and without a missing element in an alternating fashion with a blank screen. • Results showed that the pictures had to alternate a number of times before the change was detected. • When a cue is added to show where to attend, observers noticed change more quickly.

  33. Change Detection - continued • Change blindness also occurs for film shots. • People are “blind” to the fact that they experience change blindness. • Real objects in the environment change with some type of movement, which is why we normally don’t experience change blindness.

  34. Video: Change Blindness

  35. Figure 6-18 p139

  36. Figure 6-19 p139

  37. IS Attention Necessary for Perceiving Scenes? • Experiment by Li et al (2002) • Observers performed one of three tasks • Central task - determine whether letters flashed in the center of the screen are the same • Peripheral task - determine whether faces flashed to the side of the screen are male or female • Dual task - do the same as the peripheral task and determine the color of a disc

  38. Figure 6-20 p140

  39. Figure 6-21 p140

  40. The Distracting Effects of Task-Irrelevant Stimuli • Task-irrelevant stimuli are stimuli that do not provide information relevant to the task • Foster and Lavie (2008) • Load theory of attention • Perceptual capacity • Perceptual load • Low-load tasks

  41. Figure 6-22 p141

  42. Figure 6-23 p142

  43. Attention and Experiencing a Coherent World • Binding - process by which features are combined to create perception of coherent objects • Binding problem - features of objects are processed separately in different areas of the brain • So, how does binding occur?

  44. Figure 6-24 p142

  45. Feature Integration Theory • Preattentive stage - features of objects are separated • Focused attention stage - features are bound into a coherent perception

  46. Figure 6-25 p143

  47. Feature Integration Theory - continued • Illusory Conjunctions - features that should be associated with an object become incorrectly associated with another. • Experiment by Triesman & Schmidt • Stimulus was four shapes flanked by two numbers. • Display flashed briefly, followed by a mask. • Task was to report numbers first followed by shapes at four locations.

  48. Figure 6-26 p143

  49. Figure 6-27 p144

  50. Feature Integration Theory - continued • Triesman & Schmidt results showed that: • incorrect associations of features with objects occurred 18% of the time. • asking observers to focus on the target objects eliminated this effect. • Balint’s syndrome - patients with parietal lobe damage show lack of focused attention results in incorrect combinations of features

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