PSYCH 240 1st Edition Lecture 2 Outline of Last Lecture • Introduction + Methodology and History of Cognitive PsychologyOutline of Current Lecture • What is Perception• 3 major stages of perception• Major phenomena• Theories of Perception• Direct vs. constructivist• Bottom-up vs. top-down• Depth Perception• ProblemCurrent Lecture• Perception: the means by which info acquired from the environment via sense organs is transformed into experiences of objects, events, sounds, tastes, etc.• 3 stages of perception• Distal Stimulus: the thing at a distance that you’re trying to perceive• Briefcase on a table 15ft away, the distal stimulus is the actual briefcase (far away, not near your sensory organs)• Proximal Stimulus: pattern distal stimulus makes on your sensory organs• Pattern that looking at the briefcase generated unto your retina (close to you – on your sensory organs)• Percept : your internal mental representation of what it is that you’re perceiving• In your mind’s eye you see a briefcase• Major phenomena• Lack of correspondence: when percept does not correspond to distal stimulus (when our thoughts don’t accurately correspond to what we’re looking at)• Perceptual illusions • Paradoxical correspondence: when proximal stimulus (the patternthe distal stimulus is making on your sensory organs) does NOT correspond to distal stimulus but percept DOES (you still constructan accurate mental representation) – it’s an anomaly• Moving objects, moving eyes • Perceptual Constancy: our perception of an object’s features remains constant even when viewpoint ( and proximal stimulus) changes• Perception of size doesn’t change w/ distance• When someone walks toward you, you don’t perceive them as growing. Your brain perceives them as moving• Perception of color doesn’t change w/ light• When light shines on a colored fabric, we still know that the robe is all one color despite the light changing the color (makes it look yellowy or lighter)• Perception of shape doesn’t change w/ angle• A flat door looks like a rectangle when closed but looks completely different when partially open. We still perceive it as the same door.• Theories of Perception• Direct vs. Constructivist• Direct (stimulus) Perception• “ask now what’s inside your head but what your head is inside of” – JJ Gibson• Our perception is extremely well adapted to pick upall the subtle cues in the environment and directly deliver an accurate percept • Environ provides all necessary cues• Our brains are pre-wired to pick up on cues• Stimulus is almost always unambiguous• Constructivism• Perception uses data from the world AND our prior knowledge and expectations• Sensory information is often ambiguous• Must rely on knowledge/expectations to figure out what it really is that we’re looking at• Our expectations influence what we see• Bottom-up vs. top-down• Bottom-up processing: processing that is driven by the external stimulus, rather than internal knowledge• Direct perception claims perception is purely bottom-up• Top-down processing: processing that is driven by knowledge and expectations• Constructivism: bottom-up AND top-up processing• Example: Depth Perception– How do we perceive depth when our retinas are flat• Problems• Distal stimulus (the world) is 3D• Proximal stimulus (on retina) is 2D• Perceptual experience is 3D • This is an example of paradoxical correspondence• How it works? • Exploit environmental cues to recover depth• Depth cues: • Linear perspective (monocular)• Shape - texture gradience (monocular)• Relative size (monocular)• Interposition (monocular)• Shadows (monocular)• Retinal disparity - the way that your left eye and your right eye view slightly different images• Accommodation (lens flat = far away, lens wide = something close)• Convergence