Perception Lec
Perception Lec
Perception Lec
• 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
Brief Story
• 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!!