KMF 1023 Cognitive Psychology Visual Perception PDF

Unit 3 Part 2 Visual Perception KMF 1023 COGNITIVE PSYCHOLOGY Universiti Malaysia Sarawak 1 In this topic, we will learn: continuation of Top-down Processing: Gestalt Approach Heuristics vs Algorithm Evidence that perception is a...

Unit 3 Part 2 Visual Perception KMF 1023 COGNITIVE PSYCHOLOGY Universiti Malaysia Sarawak 1 In this topic, we will learn: continuation of Top-down Processing: Gestalt Approach Heuristics vs Algorithm Evidence that perception is an intelligent activity – Some behavioral and physiological evidence 2  Top Down Processing: Gestalt principles Perceptual organization also occurs for hearing, speech segmentation etc. Gestalt approach applies to speech – We group or organize speech into meaningful words according to our knowledge of the language (top down perception of gestalt principles in speech) Speech Segmentation – When we listen to someone speaking in a foreign language, the words seem to be continuous, but to the speaker of the language who understands what the word means, the words are separate. – Eg. “thank you”, “terima kasih”, “xiexie”, “kamsiah”, “tochear”, “arigatogozaimas”, “merci”, “gracias denada” – Eg. “I scream, you scream, we all scream for ice cream” 3 Figure 3.36 (p. 81) Sound energy that results from saying the two words “Speech Segmentation.” Notice that it is difficult to tell from this record where one word ends and the other begins. (Speech signal courtesy of Lisa Saunders) 4  Gestalt principles Gestalt principles provides us with “best guess” predictions May not be accurate 100% of the time In problem solving, there are 2 approaches: 1) Heuristics – Best guess answer to a problem (shortcut approach) – Fast, not time consuming – May not result in a correct solution every time 2) Algorithm – A procedure that is guaranteed to solve a problem – Takes time (STEP BY STEP PROCEDURES) 5 Figure 3.37 (p. 81) What lurks behind the three? What procedures (Algorithm vs. Heuristics) are involved in the perceptual system if you are to solve this problem? 6 Figure 3.38 (p. 82) It is two strangely shaped tree stumps, not an animal! 7  Heuristic for perception Figure 3.45 (p. 88) In the distance, the Cathedral of Learning on the campus of the University of Pittsburgh rises from behind a tree. Because of the occlusion heuristic, we perceive this building a continuing behind the tree. Similarly, we don’t see the person in the foreground (your author) as being chopped into little pieces by the fence, but we see his body as continuing behind the fence. 8  Why is perception is an intelligent activity? Gestalt principles- demonstration of how humans are capable of intelligent grouping of information Try getting a computer to do the same thing! 9  Main Components in Visual Perception (Human vs Computer) Retina Brain Scene Image Acquisition Image Processing Light Computer Camera 10 Why is perception so hard for computers? (The heuristics that humans use to give them the advantage over computers) Four reasons: – Stimulus received from our receptors may not be clear (ambiguous) – Objects need to be separated intelligently – Parts of an object can be hidden – Changes in lightness and darkness can be unclear Humans have built-in intelligence in our visual perceptual system, an advantage that computers do not have Though we may not be 100% accurate all the time… 11 Figure 3.43 (p. 86) For this scene, it would be difficult for a computer to sort out which changes are due to properties of different parts of the scene and which are due to changes in illumination. 12  Where does our perceptual intelligence comes from? Knowledge from experience (memories formed from birth)) Or Neurons in our brains that respond to faces and other objects in the environment. These neurons turn the brain into a processor that is adapted to each object that we face in the environment. Neurons specialized through: – Evolution – some neurons may have evolved to respond to specific situations/stimuli exist in the environment – Experience – involve adaptation of neurons to the environment 13  Where does our perceptual intelligence comes from? An experiment to support Neurons specializing through experience – Experience-dependent plasticity Causes neurons to develop so they respond best to the types of stimulation to which the person has been exposed (bottom-up process) – Study with animals and humans – In humans, experience-dependent plasticity is located in temporal lobe in FFA (fusiform face area) – FFA is activated when a person looks at faces 14  Experience-dependent plasticity Experiment Experiment by Gauthier (1999) Used FMRI to measure the activity in FFA when subjects in the experiment are shown human faces vs “Greebles” – Greebles- computer generated images vs 15  Experience-dependent plasticity Experiment Results (before training) – FFA neurons are activated and respond to human faces, less to Greebles Then subjects were given training to recognise “Greebles” over 3-4 days so they became “Greebles expert” Results (after training) – FFA neurons respond almost as well to human faces and Greebles With experience and new learning, neurons can become specialised to respond to particular stimulus => experience-dependent 16 plasticity Where does our perceptual intelligence comes from? Brain “intelligent Knowledge stored processing” from all our experiences of the Evolution Experience- world dependent (Top-down plasticity to processing) respond to new experiences (eg. Greebles experiment) (Bottom-up processing) => Increase our chance of perceiving accurate information about our environment 17  Summary Top Down Processing involves: – Gestalt principles of organization – Heuristics (shortcut) and algorithm approaches 4 reasons why visual perception is hard for a computer compared to a human: – Stimulus received from our receptors may not be clear – Objects need to be separated intelligently – Parts of an object can be hidden – Changes in lightness and darkness can be unclear There are neurons in the temporal lobe (eg. FFA area) which can be trained to specialize in perceiving human faces – evidence for process of visual perception in the brain Perception = TD & BU processing 18  Readings for this lecture: Textbook by Goldstein- Chapter 3 (p. 55-95) Create a Concept Map/ Mindmap of Chapter 3 Participate in COGLAB – Visual Search 19 Sekian, Terima Kasih & Good Luck 20