Top-Down versus Bottom-Up Perception Perceive the whole and then individual parts as needed. Experience-driven as opposed to stimulus or input-data driven. Quick and highly inferential but also a source of misperception. Bottom-up Perceive the individual parts and organize them into a whole, if possible. Information available in the stimulus itself. Arranged by Dr. Gordon Vessels 2005

Form Perception & Feature Analysis Bottom-Up Processing Relies on properties of the stimulus such as patterns of light and dark areas. Top-Down Processing Relies on higher-level information such as prior knowledge and experience. What is in this picture? Modeled after a PPT slide created by Kevin Richardson in 1998 and made available through the American Psychological Society

Bottom-Up Processing Perception Stimuli Input Stimuli Processing Prior Knowledge, Experience, etc. Perception Stimuli Processing Stimuli Input Created by Dr. Gordon Vessels 2005

David Marr’s Computational Bottom-Up Approach Marr wanted to understand mechanisms of vision rather than just behaviors associated with it. …he wanted to link neurophysiology with psychology. He took an information processing view of the mind… …and aimed to describe perception in terms of computations on sense data… …to extract high level visual experience. Source: Bell, Vaughan (2004). Perception and perceptual distortion. A PPT presentation retrieved at http://www.cardiff.ac.uk/psych/home/bellv1/ Used here with the author’s written permission. Slide arrangement by Vessels, 2005.

Marr’s Stages of Visual Processing Marr proposed there were distinct stages of processing in visual perception: Stage 1: Raw Primal Sketch Stage 2: Complete Primal Sketch Stage 3: 2½D Sketch Stage 4: Full 3D Representation Source: Bell, Vaughan (2004). Perception and perceptual distortion. A PPT presentation retrieved at http://www.cardiff.ac.uk/psych/home/bellv1/ Used here with the author’s written permission. Slide arrangement by Vessels, 2005.

Stage 1: Raw Primal Sketch This involves the extraction of information regarding edges and intensity changes. Source: Bell, Vaughan (2004). Perception and perceptual distortion. A PPT presentation retrieved at http://www.cardiff.ac.uk/psych/home/bellv1/ Used here with the author’s written permission. Slide arrangement by Vessels, 2005.

Stage 2: Complete Primal Sketch After the Raw Primal Sketch… Marr [proposed]… we create a Complete Primal Sketch by grouping surfaces and common areas. The Gestalt Psychologists of the early 19th Century demonstrated many different ways in which we can group objects. Source: Bell, Vaughan (2004). Perception and perceptual distortion. A PPT presentation retrieved at http://www.cardiff.ac.uk/psych/home/bellv1/ Used here with the author’s written permission. Slide arrangement by Vessels, 2005.

Stage 3: 2½D Sketch After gaining information about groupings and surfaces, the viewer needs some spatial information. Marr called this stage the 2½D Sketch to emphasis that this stage does not give a full 3D representation. Rather, just an estimate of the spatial locations of objects and materials in relation to the viewer. Source: Bell, Vaughan (2004). Perception and perceptual distortion. A PPT presentation retrieved at http://www.cardiff.ac.uk/psych/home/bellv1/ Used here with the author’s written permission. Slide arrangement by Vessels, 2005.

2½ D Sketch: Depth Cues We perceive much information from which we infer depth: Binocular disparity Texture gradients Occlusion Convergence Relative Size Source: Bell, Vaughan (2004). Perception and perceptual distortion. A PPT presentation retrieved at http://www.cardiff.ac.uk/psych/home/bellv1/ Used here with the author’s written permission. Slide arrangement by Vessels, 2005.

Stage 4: 3D Representation The final stage of Marr’s theory. A full 3D description of our spatial environment involving the identification of the structure of objects and materials in our visual field. It allows us to work out the 3D environment from a non-egocentric point-of-view. Source: Bell, Vaughan (2004). Perception and perceptual distortion. A PPT presentation retrieved at http://www.cardiff.ac.uk/psych/home/bellv1/ Used here with the author’s written permission. Slide arrangement by Vessels, 2005.

Gregory on Top-Down Perception Gregory proposes that we use our prior “experience of the world to shape how we perceive” stimuli we encounter in it. His theory of perception is called Top-Down, Which means we use activated conceptual schemas and memory networks (our stored knowledge), more or less automatically and subconsciously, to shape our perceptions or to interpret our sensory input ― sometimes correctly and sometimes not. He confirmed many of his theoretical propositions using visual illusion research. Primary source Bell, Vaughan (2004). Perceptions and perceptual distortions, a PPT show accessed at http://www.cf.ac.uk/psych/home/bellv1/conf/VaughanPerceptionLecture2004.ppt#1. Written permission granted 5-5-05.

Top-Down Processing Perception Stimuli Processing Stimuli Input Culture Social Class Values Beliefs Prejudices Attitudes Personality Temperament Occupation Education Prior Stimuli Perceived Prior Knowledge, Experience, etc. Immediate Mental Set Present Fatigue Energy Level Presence of Authority Needs, Moods Mental Health Knowledge Vocabulary Long-term Memory Schemas Specific Life Experiences Perception Stimuli Processing Stimuli Input Created by Dr. Gordon Vessels 2005

If all of these people were at the same football game, who among them was most likely to have perceived what actually happened on a controversial play where the receiver may have fumbled the ball before his knees touched the ground? Whose perceptions were the most bottom up? Whose perceptions were the most top-down and thus influenced and quickened in terms of inference by their present needs, biases, and heightened emotion? Whose perception may have been the most accurate and objective based on his or her knowledge of the game? When the head referee reviewed the replays, did he use top-down or bottom-up perception primarily? What top-down influence may have made it possible for his perceptions to have been highly accurate? Did these people literally see something different? Do they really believe what they claimed to have seen?

What do you see. The word liar in script or cursive What do you see? The word liar in script or cursive? A face looking down? Those shown artwork with faces were more inclined than others to see the word liar. What do you see? A face looking down? The word Liar in script or cursive? Those who first read stories about deception were more inclined than others to see the word Liar. Arranged by Dr. Gordon Vessels 2004

Top-Down & Bottom-Up Processing Prior Knowledge, Experience, etc. Perception Stimuli Processing Stimuli Input Created by Dr. Gordon Vessels 2005