PY 105 Chapter Notes - Chapter 2: Detection Theory, Absolute Threshold, Color Vision
Photoreceptors: Rods and Cones
• Contain special pigment proteins that change their tertiary structure upon absorbing light
• Each protein, opsin, is bound to one molecule and contains one molecule of retinal
• Upon absorbing a photo of light, retinal is converted to all-trans form
• Release neurotransmitter glutamate (inhibitory effects on bipolar cells)
• Night vision - rods
o Sensitive to dim light and motion
• Cons - abundant light
o Color vision and high acuity vision
Defects in Visual Acuity
• Emmetropia - normal vision
• Myopia - nearsightedness
o Too much refraction
• Hyperopia - farsightedness
o Too little refraction
Vision: Information Processing
• Neurons in visual cortex fire
• Feature detection theory - explains why a certain area of the brain is activated when looking at a
face or words
• Parallel processing - many aspects of a visual stimulus are processed simultaneously instead of in a
step-by-step fashion
General Sensory Processing
• Absolute thresholds
o The minimum stimulus intensity required to activate a sensory receptor 50% of the time is
called the absolute threshold
• Difference threshold
o Minimum noticeable difference between any two sensory stimuli, 50% of the time
• Weber's law - two stimuli must differ by a constant proportion in order for their difference to be
perceptible
o Must differ in weight by 2%
Signal Detection Theory
• Predicts how and when someone will detect the presence of a given sensory stimulus amidst all of
the other sensory stimuli in the background
o Hit - signal present and detected
o Miss - signal present and not detected
o False alarm - signal not present and person detected it
o Correct rejection - not present and person didn’t think it was
Gestalt Psychology
• The whole exceeds the sum of its parts
• Rather than seeing lines, colors and shadows, they perceive the whole - face, table, dog
• Bottom up processing - begins with sensory receptors and works up to complex integration of
information in the brain
• Top down processing - occurs when brain applies experiences and expectations to interpret
sensory information
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Document Summary
Defects in visual acuity: emmetropia - normal vision, myopia - nearsightedness, too much refraction, hyperopia - farsightedness, too little refraction. Vision: information processing: neurons in visual cortex fire. Two classes of hormones: hydrophilic, peptides, amino-acid derivatives, must bind to receptors on cell surface, hydrophobic, steroid hormones, must bind to receptors in cellular interior. Insulin secreted by beta cells of pancreatic islets of langerhans in response to elevated blood glucose levels: amino acid derivatives, derived from single amino acids, contain no peptide bonds. Stick to proteins: hydrophobic molecules synthesized from cholesterol in ser, cannot dissolve in plasma, diffuses through plasma membrane to bind with a receptor in cytoplasm, exerted slowly. Steroid hormone receptor complex is transported into nucleus. Tropic hormones - hormones that regulate hormones: example, adrenocorticotropic hormone (acth) is secreted by anterior pituitary. Stimulates increased activity of the portion of adrenal gland called the cortex: the cortex secretes cortisol, regulates stress and serum [glucose, negative feedback.
