1. Perception zWe have previously examined the sensory processes by which stimuli are encoded. zNow we will examine the ultimate purpose of sensory information zPERCEPTION - the conscious representation of the external environment.

2. Perceptual Organization zSome of the best examples that perception involves organization of sensory input was provided by the Gestalt Psychologists. zGestalt psychologists hypothesized that “the whole is greater than the sum of the parts.” zThey were interested in showing the global nature of our perceptions

3. Gestalt Grouping Principles zGestalt theorists argued that our perceptual systems automatically organized sensory input based on certain rules. zProximity zSimilarity zClosure zGood Continuation zCommon Movement zGood Form

4. Figure and Ground zGestalt Psychologists also thought that an important part of our perception was the organization of a scene in to its: zFigure - the object of interest zGround - the background

5. Depth Perception zOne of our more important perceptual abilities involves seeing in three- dimensions zDepth perception is difficult because we only have access to two- dimensional images zHow do we see a 3-D world using only the 2-D retinal images?

6. Depth Perception Cues zCue - stimulus characteristics that influence our perceptions zWe are able to see in 3-D because the visual system can utilize depth cues that appear in the retinal images.

7. Types of Depth Cues zDepth cues are usually divided into categories, we will consider two types of depth cues: zMonocular - depth cues that appear in the image in either the left or right eye zBinocular - depth cues that involve comparing the left and right eye images

8. Monocular Depth Cues zOcclusion zRelative image size zlinear perspective zTexture gradient zPosition relative to Horizon zDifferential lighting of surfaces (Shading)

9. Relationship Between Perceived size and Perceived Depth zTo perceive the size of objects accurately we must also perceive their distance accurately. zThus, many visual illusions occur simply because a particular image lacks sufficient depth cues. This figure shows that image size depends upon both object size and distance Retina Pupil Image A B A

10. Ames Room zThe Ames room is designed so that the monocular depth cues give the illusion that the two people are equally far away

11. Other Size-Distance Illusions zIn each of these examples, the top and bottom lines are actually the same length. zIn each case the top line looks longer. zWhy? (a) Müller-Lyer illusion (b) Ponzo illusion

12. Muller-Lyer Illusion zPerceptual psychologists have hypothesized that the top horizontal line looks longer because it also looks farther away. zSpecifically, the inward pointing arrows signify that the horizontal line is closest to you, and the outward pointing arrows signify the opposite case.

13. Ponzo Illusion zConverging lines indicate that top line is farther away than bottom line

14. Binocular Depth Cues zMonocular depth cues allow us to see in 3-D with the view of only one eye, but our best depth perception occurs if we look through both eyes. zThis is because our right and left eyes see a slightly different view of the world. zThis difference between the image in the two eyes is know as Binocular Disparity.

15. Binocular Stereopsis zBinocular Stereopsis - the perception of depth based on retinal disparity zPsychologists typically study binocular stereopsis with the use of stereograms. zStereogram - stimulus consisting of a left eye and a right eye image. When these two images are fused, the Illusion of depth is created.

16. Stereogram

17. Autostereogream zAnother way to create the illusion of depth through binocular stereopsis is with an Autostereogram. zAn autostereogram is formed by superimposing two repeating patterns zThe two patterns are slightly offset, and when viewed properly, this offset is seen as a binocular disparity.

18. Autostereogram

19. Perceptual Constancy zWhen viewing conditions change, the retinal image changes even if the objects being viewed remain constant. zExample: as a person walks away from you their retinal image decreases in size. zimportant function of the perceptual system is to represent constancy in our environment even when the retinal image varies.

20. Size Constancy zCylinders at positions A and B are the same size even though their image sizes differ zThe depth cues such as linear perspective and texture help the visual system judge the size accurately Point A Point B

21. Shape Constancy zIt is hard to tell if the figure on the upper right is a trapezoid or a square slanted backward. zIf we add texture, the texture gradient helps us see that it is actually a square.

22. Attention: Combining the Elements of Perception zWe can not be consciously aware of all the perceptual information available to us at any one time. zThus, we have the ability to enhance some aspects of our perception while ignoring others. zThis selective process is know as attention.

23. Preattentive processing zSome aspects of our perception are under our conscious attentive control. zExample: In a large crowd, we can concentrate on listening to some people and ignoring others. zHowever, other perceptual processes occur automatically and we can not consciously control them.

24. Feature Integration zFeature detection is an example of a preattentive perceptual process, and can be done in parallel zFeature Integration, seems to require attention and most be performed serially.

25. Feature Integration Feature- detection files Line slant Color Etc. Feature integration Stage 1 Stage 2 Stimuli Conscious perception of stimulus (a red X) V V X X

26. Feature Pop Out zThe slanted line amongst vertical lines Pops Out, but the cross amongst horizontal and vertical lines does not pop out. (a) (b)

27. The Stroop Effect: Learned Automaticity zSome abilities which once required attention can become automatic through practice. zAn example of such learned automaticity is found in the Stroop Intereference Effect. zStroop found that the act of reading could interfere with your ability to perform simple perceptual distinctions like naming colors.

28. Stroop Effect zIn Stroop’s experiment, observers were asked to look at a word and name the color of the ink used to write that word. zStroop found that if the meaning of the word was different than the color of the ink, observers were less successful at naming colors. GREEN RED BLUE BLACK BLUE RED GREEN BLACK RED BLUE RED BLUE GREEN BLACK GREEN BLUE BLACK RED BLUE GREEN TRUCK TOP COUCH HAND COUCH TOP TRUCK TOP COUCH HAND (a) (b)(c)(d)