Week 4

Sensation: Stim of sense organ Transduction: receptors convert physical from environment to signals for brain to interpret

Interpretation of a sensation –> mental representation

Sensitivity to prolonged stim tends to decline over time as one adapts to current conditions

Study of how physical stim affect the senses

Minimal intensity needed to barely detect a stim 50% of the time

How responsive one is to faint stim

Differentiating btw two stim (e.g. two similar tones)

Minimal change in a stim that can barely be detected

Amount of change needed for change to be noticed is constant ratio of the original stim

Response to a stim depends on person’s sensitivity to stim and a person’s decision critereon

1) Light passes through CORNEA (clear protective layer around eye) 2) Light passes through PUPIL (hole in the IRIS, the colored part of the eye that controls how much light is let in) 3) Light passes through LENS, which is shaped by eye muscles so the light is focused on the RETINA in a process called ACCOMMODATION (lens flatter for objects further away, lens more curved for objects nearby) 4) Retina lined with PHOTORECEPTOR CELLS called RODS and CONES 5) Signals from rods and cones transducted to brain via the OPTIC NERVE (OPTIC DISK is the beginning of the nerve in the eye)

Myopia/nearsighted - eyeball too long –> image focused in FRONT of retina Hyperopia - eyeball too short –> image focused BEHIND retina

• Peripheral and night vision, brightness • More rods than cones (~120M rods) • Distributed evenly in retina except for area in the macula called the FOVEA • No rods in fovea –> reduced clarity in low light but increased sensitivity to light in periphery

• C words - “Clarity and Color” • ~6M cones; concentrated in the FOVEA but sparse in macula/retina –> we see things much clearer if we look right at them • 3 different cones for 3 different wavelengths: L-cones (long - red), M-cones (medium - green), S-cones (short - blue) • Missing cones –> color blindness

We perceive color by combining RGB wavelengths

Pairs of cone types work against each other

Opponent process theory: cones are together in opposing pairs: red/green, yellow/blue, black/white - Cells stimulated by green inhibit the cells stimulated by red - When changed, the previously inhibited red cells fire, while the green PREVIOUSLY-stimulated cells are tired and don’t fire –> we see red

rods/cones –> bipolar cells –> retinal ganglion cells –> lateral geniculate nucleus (part of thalamus) –> area v1 –> other parts of the brain NOTE: bunded RGCs form the optic nerve

Dorsal: “where” – where an object is and its movement; upper pathway to parietal lobe Ventral: “what”/”how” – shape and identity of an object; lower pathway to temporal lobe Purpose: Neurons in area v1 only perceive small details like edge –> signals to regions farther from V1 respond to more complex features

Visual agnosia: inability to recognize objects Prosopagnosia: inability to recognize faces

Injured ventral stream –> couldn’t recognize objects

Sensory receptors pick up signals and send them to the brain

Perceiving things based on your prior knowledge of the world

• Can be seen w one eye • Linear perspective/vanishing point, light and shadow, interposition, relative height, relative size, texture gradient