Lecture 1 (Visual Attention) V2 PDF

3/27/23 A/Prof Piers Howe https://psychologicalsciences.unimelb.edu.au/research/msps-researchgroups/visual-cognition-behaviour/lab#people-contacts 1 0 1 Sensation & Perception — I have the very real privilege of teaching the Sensation & Perception section of this subject — This section will occ...

3/27/23 A/Prof Piers Howe https://psychologicalsciences.unimelb.edu.au/research/msps-researchgroups/visual-cognition-behaviour/lab#people-contacts 1 0 1 Sensation & Perception — I have the very real privilege of teaching the Sensation & Perception section of this subject — This section will occur in weeks 5-7 — During this time, we will cover the following topics — Visual attention — Object and scene perception — Motion perception — Colour perception — Depth and size perception — Audition 2 2 3 3 1 3/27/23 Tutorial Required reading — There will also be two tutorials focusing on my content — These will occur in Weeks 6 and Week 7 — The first tutorial will focus on change blindness — Change blindness is our inability to notice changes to a visual scene which, in retrospect, seem obvious. — In this tutorial, you will conduct a change blindness experiment to test the predictions of a theory proposed by Rensink, O’Regan & Clark (1997) — To support this tutorial there is a required reading — Rensink, O’Regan & Clark (1997) describe a series of change blindness experiments. Their Experiment 2 is very similar to the one that you will conduct — It is available on Readings Online on the subject website. — Please do this reading before the tutorial — The reading is examinable — It is the only required reading for my section of the subject. 4 4 5 5 2nd Tutorial Additional Readings — The second tutorial will occur in Week 7 — It will focus on visual search — In this tutorial, you will conduct two visual search experiments to test two competing theories of visual search — At the end of the tutorial, you will be able to decide which theory provides the better account of visual search. — There is no required reading, but Wolfe, Friedman-Hill and Bilsky (1994) is an optional reading that supports the tutorial and is also located under the Readings Online tab. — (Note that this reading is incorrectly referred to as Wolfe & Bilsky (1994) in Readings Online i.e. middle author is missing.) — Because there are no additional required readings, I have made my slides comprehensive. — This means that, in addition to the sole required reading, the slides are all you need. — My slides are examinable. — This is how I ensure that you learn an appropriate amount of content. 6 6 7 7 2 3/27/23 Additional Support My Lecture Style — If you find the content of my lectures difficult, I suggest that you consult a textbook. — My lectures are most similar to Sensation & Perception 10th Edition by Goldstein and Brockmole — But almost any “Sensation & Perception” textbook will cover similar material, so would be suitable… — I want to take the opportunity to help you engage in active learning. — Meredith told you about this in her section. — You learn most when you answer questions about what you have just seen. — Therefore, I have broken each lecture into two sections and put questions after each section. — Please actually write down your answers. — …and there are a lot of them. — I will provide the answers in the next instalment. 8 8 9 9 Learning objectives — In this lecture, I am going to discuss visual attention — I am going to cover the following topics — What is attention? — What directs our attention? — What are the effects of attention? — The binding problem — Change blindness 11 10 11 3 3/27/23 What is attention? Why is attention needed? — Attention is the ability to preferentially process some parts of a stimulus at the expense of processing of other parts of the stimulus. — For example, if you focus your attention on my face, you will preferentially process my face at the expense of processing other objects in the scene. — Consequently, you will perceive my face more clearly than other objects in the scene. — Your perceptual system has a limited capacity. — You can’t process everything in the visual scene simultaneously — For example, in front of me now there are lots of people. — I can’t look at everyone at the same time. — To avoid being overwhelmed, I pay attention to only one person at a time and ignore the rest. — Attention therefore helps us avoid becoming overwhelmed. 12 12 13 13 What is the difference between overt and covert attention? — Overt attention involves looking directly at an object — Covert attention involves looking at one object but attending to another object — Question: When might you employ covert attention? 14 14 15 15 4 3/27/23 Monitoring Attention — Unless you purposely try not to, generally you always look at (i.e. fixate) the object to which you attend — Thus, we can generally tell where someone is attending just by tracking their eye movements. — When a person looks at an object, they are said to fixate it. — The eye movements between fixations are ballistic (i.e. very fast). — These eye movements are called saccades. Pope Field 16 16 17 17 Terminology break! Learning objectives — I have been using the terms “fixation” and “saccade” but what do these terms mean? — Your eyes do not scan over a visual scene smoothly. — Instead, they jump from point to point. — They jumps are known as saccades. — The rests between the jumps, where the eyes stay looking directly at one part of the scene, are known as fixations. — What you fixate is determine by your goals and expectations. — What is attention? — What directs our attention? — What are the effects of attention? — What is the binding problem? — What is change blindness? 18 18 19 19 5 3/27/23 What directs our attention? Attentional capture — Two processes: — An initial involuntary process (mediated by attentional capture) — A subsequent voluntary process (guided by your goals and expectations) — Initially, when a scene is first presented, your fixations are captured by salient parts of the scene — This phenomenon is known as “attentional capture” and is involuntary. — After the first few fixations, you can then direct your fixations according to your goals — This process is voluntary. — Determined by salience of image/object — Salience = the quality of being noticeable — Here, attention is first directed to the red match-head as it is the most salient object in the scene. David Pacey 20 20 21 Attentional capture What Captures Our Attention? — The task was to report the orientation of the line in the square — The red circle was irrelevant. — However, because it was salient, attention was initially directed to it, and participants often reported the orientation of its line. — Basically…contrast — Regions of colour contrast or luminance contrast — Regions of size contrast + — Regions orientation contrast — Regions of motion/flicker contrast Theeuwes (1992) 22 22 21 23 23 6 3/27/23 Color/Luminance Size/Texture Visual Scene Orientation Motion 25 Parkhurst et al. (1992) 24 24 25 Scan Paths What directs our attention? — Saliency determines what we attend to first (i.e. the first few fixations)… — …after that what we attend to is determined by cognitive factors such as the observer’s goals and expectations. Yarbus (1967) (a) Unexpected, 1884-1888, Ilya Repin (Bridgeman Images) (b) James R. Brockmole 27 26 26 Saliency Map 27 7 3/27/23 Fixation Duration and Repeated Fixations Expectations — Fixations not only determined by goals — Your expectations also determine your fixations — If an object is unexpected, you will fixate on it for longer and fixate it more often Semantically consistent object 29 Vo & Henderson (2009) 28 28 29 Fixation Duration and Repeated Fixations Fixation Duration and Repeated Fixations Semantically inconsistent object Syntactically inconsistent object 30 Vo & Henderson (2009) 30 31 Vo & Henderson (2009) 31 8 3/27/23 What directs our attention? Learning objectives — Summary — What is attention? — What directs our attention? — Initially, fixations are often involuntary — attentional capture — What are the effects of attention? — What is the binding problem? — Then, the fixations are voluntary, goal directed and are influenced by our expectations — What is change blindness? 32 32 33 33 Attention Speeds Responses To Stimuli What Are the Effects of Attention? Valid (40%) Invalid (10%) — Attention speeds responses — Attention can influence appearance — Attention can influence physiological responding Neutral (50%) Time + X X X Posner (1978) 34 34 35 35 9 3/27/23 Attention Can Change the Apparent Contrast of an Object Response Time (ms) Required to report orientation of higher contrast grating 400 35 0 When both gratings were of equal contrast, typically reported orientation of cued grating… 300 2 50 2 00 …suggesting that cued grating appeared to be higher contrast 0 150 Valid Invalid Neutr al Carrasco et al. (2004) Posner (1978) 36 36 37 37 Attention Can Change the Appearance of an Object Attention Can Influence Physiological Responding — Attention can also affect the physiological response to a stimulus. — Essentially, neurons in the brain respond more strongly to attended stimuli than to unattended stimuli. — More about that in a few weeks… — So Carrasco et al. (2004) showed that attention can make objects appear to have a higher contrast. — Other studies have shown that attention can make objects appear bigger, faster, and more richly coloured (Anton-Erxleben et al., 2007; Fuller & Carrasco, 2006; Turatto et al., 2007). — Essentially, attention makes perception more vivid. — Attention affects not only how quickly a person can respond to a stimulus but also the appearance of the stimulus. 38 38 39 39 10 3/27/23 Pop Quiz Why is attention needed? — Without looking at the previous slides, write down your answers to the following questions: — Your perceptual system has a limited capacity. — You can’t process everything in the visual scene simultaneously. — Why is attention needed? — What directs your attention? — To avoid being overwhelmed, you pay attention to only part of the scene at a time and ignore the rest. — Attention therefore helps you avoid becoming overwhelmed. — What are the effects of attention? 40 40 41 41 What directs our attention? What Are the Effects of Attention? — What you attend is usually determined by where you fixate. — Initially, fixations are often involuntary and are determined by the saliency of the scene (i.e. attentional capture). — Then, the fixations are voluntary, goal directed, so are influenced by your goals and expectations. — Attention speeds responses — Attention can influence appearance — Attention can influence physiological responding 42 42 43 43 11 3/27/23 The Binding Problem Learning objectives — Different aspects of a stimulus are processed independently, often in separate brain areas. — For example, motion is processed by the dorsal stream and form is processed by the ventral stream — What is attention? — What directs our attention? — What are the effects of attention? — What is the binding problem? — What is change blindness? Dorsal Stream Ventral Stream Selket 44 44 45 45 The Binding Problem The Binding Problem — The problem becomes more difficult when there are multiple objects — The issue of how an object’s individual features are combined (i.e. bound) to create a coherent percept is known as the binding problem. — How are you able to see a red vertical bar and a green horizontal bar? — Why don’t you see a green vertical bar and red horizontal bar? — How are you able to associate the correct colour with the correct object? 46 46 47 47 12 3/27/23 Illusory Conjunctions Feature Integration Theory — A prediction of FIT is that if attention is inhibited, features from different objects will be incorrectly bound together. — Treisman & Schmidt (1982) showed that such illusory conjunctions occur — They presented character strings very briefly (95-168 ms) followed by noise mask. — The primary task was to report the two numbers. — Then O’s were asked to report coloured letters. — O’s often associated the wrong colour with the wrong letter — Such incorrect bindings are known as illusory conjunctions — Feature Integration Theory (FIT) suggests that the binding problem is solved by attending to only one location at at time. — Crucially, only features associated with that location are processed, so only those features are bound together. — This avoids binding features from different objects. 48 48 49 49 Balint’s Syndrome Illusory Conjunctions 9 6 5-1 8m s — RM is a patient who has parietal lobe damage. — As a result has a condition called Balint’s syndrome. — When multiple objects are present, RM has difficulty focusing attention on a single object. — When shown two letters, each with a different colour, reported the wrong letter colour combinations on 23% of the trials, even when allowed to view the letters for as long as 10 seconds! — So RM very prone to experiencing illusory conjunctions because he could not focus attention on just a single object. Noise Mask 1s r ia Va b le 9XTA5 Ti m e Treisman & Schmidt (1982) 50 50 51 51 13 3/27/23 Visual Search Visual Search — Some forms of visual search require binding to occur. — For example, binding is required if the target contains the same features as the distractors. Target features: red horizontal — In the next slide, determine as quick as you can if there is a red horizontal rectangle anywhere on the slide. Distractor features: red, green horizontal, vertical Target: — If the target differs from the distractors only by its particular conjunction of features then that is a conjunction search — FIT predicts that in conjunction searches attention needs to be applied to each object in turn (i.e. one at a time) to determine whether or not the attended object is the target — Thus, these searches are predicted to be very slow 52 52 53 53 Visual Search Is the target present? — Other types of visual search can be performed without solving the binding problem. Target features: red Distractor feature green — Here the target contains a feature (red) that the distractors do not contain — This is known as a feature search — FIT predicts that because binding does not need to occur, attention does not need to be applied to each item in turn. — Thus, such searches are predicted to be fast. 54 54 55 55 14 3/27/23 Is the target present? Visual Search — In the next slide, determine as quick as you can if there is a red square anywhere on the slide. Target: 56 56 57 57 Take Home Message Learning objectives — Visual searches that require the binding problem to be solved (e.g. conjunction searches) are predicted to be slow — Visual searches that don’t require the binding problem to be solved (e.g. feature searches) are predicted to be fast. — What is attention? — What directs our attention? — What are the effects of attention? — What is the binding problem? — What is change blindness? 58 58 59 59 15 3/27/23 Change Blindness — Attention can also determine what we remember. — If you don’t attend to it, chances are you won’t remember it. — You are now going to be shown two images in succession. — Your task is to spot the two differences between the two images. 60 60 61 Ronald Rensink 63 61 62 62 Ronald Rensink 63 16 3/27/23 Motion Transients Change Blindness — You can remember only a few parts of a scene at one time. — Question: Why doesn’t change blindness occur all the time? — Answer: Because changes usually generate motion transients that draw attention to the location change, thereby making it easy to spot the change. — If one of those parts change, you notice the change — If some other part of the scene changes, chances are you won’t notice the change – change blindness 64 64 65 65 Motion Transients Motion Transients 66 66 67 67 17 3/27/23 Change Blindness Motion Transients — In the previous demonstration, a blank screen was inserted between images. — This meant that when the second image was shown, motion transients occurred for every part of the image not just the parts that changed. — This meant that motion transients did not guide attention to the change. — Change blindness doesn’t just happen in static pictures. — It can also occur in the real world – as demonstrated by Simons and Levin (1998) 68 68 69 69 Your Tutorial — So how easy is to to cause change blindness to occur? — This previous demonstration makes it look like it should be trivial – but it is not! — Remember: For change blindness to occur, the change needs to be missed when attention is not drawn to the location of the change but the change must then be obvious when attention is drawn to the change. — So, you can’t make small, hard-to-see changes. — You need to make large changes but do so in such a way that they are missed. — Not as easy as you might think…as demonstrated by this change blindness failure Simons & Levin, 1998 70 70 71 71 18 3/27/23 72 72 73 73 An Obvious Fail! — No one is going to miss that change! — But why? — Because you can attend to up to 4 objects at any one time and if any of those objects change, you notice the change. — But there were lots of objects. How did I know that you would attend to the red one? — Because it was salient, it stood out, it drew attention. 74 74 75 75 19 3/27/23 Your Tutorial Your Tutorial — For your tutorial, you are going to conduct a change blindness experiment — Your tutorial will focus on predicting which changes you will spot and which you will miss. — Essentially, you will try to predict which objects observers will attend to. — The catch: You are going to be using more complex and realistic scenes.. — I have recorded a video explaining what you will do in the tutorial. — It is very important that you view this video before the tutorial. — As the tutorial will be based on Experiment 2 of the required reading (Rensink et al., 1997), it is important to also do this reading before the tutorial. — I would suggest that you do this reading and view the video now while this lecture is still fresh in your mind. — Good luck! 76 76 77 77 Questions — Before the next lecture, please write down answers to the following questions. — What is the binding problem? — What is an illusory conjunction? The End — Why does Feature Integration Theory predict conjunction searches to be slow? 78 78 79 79 20