Average: 77; SD: 14.4

Exam 1 Grade Distribution

0102030405060

<29 30-39 40-49 50-59 60-69 70-79 80-89 90+Score

Number of Students

Power Functions (vs. Weber)(r)a = (s)b

• Magnitude Estimation• Steven’s Law: Power Function • Cross Modality Match

Visual system characteristics

• Retina: 120 million rods & 6 mill. Cones• Retinal distribution meaningful

System operating characteristics

• Color• Sharpness or acuity: 1 sec. line (1 inch

at 3.5 miles)• Sensitivity (range (candle at 10 mi. to

noon sun 10,000,000,000,000:1)• Differential course of adaptation

Duplex Theory of Vision

• Two systems: – Rod based

• Sensitive• Low acuity• Monochromatic

– Cone based• High threshold• High acuity• Color

Adaptation

• Overall range of light 1013 : 1• Adaptation range of eye 105 : 1

We’re not from Missouri!

• Color Vision ( Perceptual constancies/neural interactions)

• Feature Detection--the analysis of visual input– Limulus– Cats– Humans

• Top-down perceptual processes and their interactions with bottom-up

Active processing

• Sentence• Necker Cube• Gestalt principles

• The large black dog was chasing the the pretty little groundhog who was very much afraid of him across the carpet.

Feature Detection: the analysis of visual input

Bottom-up perceptual processes (lateral inhibition)– Limulus (Hartline & Ratliff)– Frogs (Matarana, Lettvin, McCullough & Pitts)– Cats (Kuffler, Hubel & Weisal)– Humans

• Top-down perceptual processes and their interactions with bottom-up

Top-down processes:Some examples and a

mechanism

Word Superiority Effect & its Mechanism

Conclusion• Perception is an active process that

tries to extract a more or less coherent iinterpretation of the world from the barrage of stimuli impacting us.

• It focuses on change (temporal or spatial).

• In order to quickly extract info from the deluge, it must distort the world to attempt to see it for what it is!!

Attention• System interrupt attracted by alternative

stimuli (dog in street)• Conscious reallocation device• Attention as limited resource• Attention as bottleneck

– Cocktail party effect : Colin Cherry– Filter theory: Donald Broadbent– Attenuation theory: Anne Triesman– Late selection theory: Donald MacKay (pennies)– Spotlight model: Michael Posner