Careers for Psychology and Neuroscience Majors Oct. 19th5-7pm in SU 300 Ballroom B

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“Top-Down” and “Bottom-Up” Processes in Perception Light & Dark Line Orientation Surfaces and Background Identity/Meaning A “Bottom-Up” System Why should this model be called into question?

“Top-Down” and “Bottom-Up” Processes in Perception Light & Dark Line Orientation COMPARE Possible Interpretations Surfaces and Background Identity/Meaning -- Sensory System -- “Top-Down” or “Look-up” System A Top-Down System

Shape Identification Requires Interaction between Top-Down and Bottom-Up Processes

Single Target - Identify shape

Single Shape/Brief Dots Shape is identified by top-down system before information in the bottom-up system gets changed

Single Shape/Brief Dots Shape is identified by top-down system before information in the bottom-up system gets changed Let’s push the system: overload top-down system AND change the signal in the bottom-up system

Single Shape/Brief Dots Shape is identified by top-down system before information in the bottom-up system gets changed Let’s push the system: overload top-down system AND change the signal in the bottom-up system What would you predict of a strictly bottom- up system?

Many targets - Identify shape inside dots

Object Substitution Strictly bottom-up system should still identify the shape! but top-down model accounts for the phenomenon: Bottom-up info gets changed before top- down process completes all that’s left in the bottom-up signal is the four dots

More Depth Cues Pictorial Depth Cues Physiological Depth Cues Motion Parallax Stereoscopic Depth Cues

Physiological Depth Cues – Two Physiological Depth Cues 1. accommodation 2. convergence

Physiological Depth Cues – Accommodation

Physiological Depth Cues – Accommodation – relaxed lens = far away – accommodating lens = near – What must the visual system be able to compute unconsciously?

Physiological Depth Cues – Convergence

Physiological Depth Cues – Convergence – small angle of convergence = far away – large angle of convergence = near – What two sensory systems is the brain integrating? – What happens to images closer or farther away from fixation point?

Physiological Depth Cues – Convergence and accommodation are reflexively linked Under what circumstances might this be a problem?

Motion Depth Cues – Motion 1. Parallax

Motion Depth Cues – Parallax

Motion Depth Cues – Parallax – points at different locations in the visual field move at different speeds depending on their distance from fixation

Motion Depth Cues – Parallax

Seeing in Stereo

It’s very hard to read words if there are multiple images on your retina

Seeing in Stereo It’s very hard to read words if there are multiple images on your retina But how many images are there on your retinae?

Binocular Disparity Your eyes have a different image on each retina –hold pen at arms length and fixate the spot –how many pens do you see? –which pen matches which eye?

Binocular Disparity Your eyes have a different image on each retina –now fixate the pen –how many spots do you see? –which spot matches which eye?

Binocular Disparity Binocular disparity is the difference between the two images

Binocular Disparity Binocular disparity is the difference between the two images Disparity depends on where the object is relative to the fixation point: –objects closer than fixation project images that “cross” –objects farther than fixation project images that do not “cross”

Binocular Disparity Corresponding retinal points

Binocular Disparity Corresponding retinal points

Binocular Disparity Corresponding retinal points

Binocular Disparity Corresponding retinal points

Binocular Disparity Points in space that have corresponding retinal points define a plane called the horopter The Horopter

Binocular Disparity Points not on the horopter will be disparate on the retina (they project images onto non-corresponding points)

Binocular Disparity Points not on the horopter will be disparate on the retina (they project images onto non-corresponding points) The nature of the disparity depends on where they are relative to the horopter

Binocular Disparity points nearer than horopter have crossed disparity points farther than horopter have uncrossed disparity