Chapter 9 Audio Perception Up to page 270 Binaural Cues cont Difference in time of arrival sound reaches near ear slightly before the far ear Reflexive Picture in textbook Neurons in the superior olive and interior colliculus binaural cues Chapter 10 Visual Perception Up to page 323 Stimulus visual light form of electromagnetic energy about 300 to 650 nm just a fraction of the electromagnetic spectrum Perceive objects at a distance without needing to come into physical contact Visible light tends to bounce off of objects which is why it s informative Visible light travels fast nothing goes faster than light except gravity in certain situations Instantaneous info about objects from far away Eyes have evolved multiple times independently of each other but look basically similar despite have no genes in common Some species have different receptors such as infrared in reptiles but are centered around the visible spectrum Color is our perception of the wavelength being reflected bounced off of an object like pitch is in regards to frequency is a continuous variable but we experience it as categorical oversimplified perception of the world not a direct copy The Vertebrate Eye Much of the movement is automatic and reflex Retina is a complex neural network Lens series of transparent onion like layers its shape can be changed by contraction of ciliary muscles Made like this so it can bend and change its shape so that you can perceive objects in focus at varying distances Cornea controls mainly how well you see objects First eyes skin cells that act as receptors to light skin folds in to form a cup which helps to locate the source of slight cup eye cup eye closes almost completely but leaves a small hole pin hole eye closes up completely with a transparent membrane to allow light in Retina the neural tissue and photoreceptors located on the inner surface of the posterior portion of the eye Photoreceptors rods and cones respond to light and transform it into an electrochemical signal transducer of eye Horizontal cells spread across photorecptors Bipolar cells connect across different layers of retina Amacrine cells same as horizontal but on the other side Ganglion cells third layer of neuron axons cluster together to form a cable optic nerve 1st layer receptors 2nd layer bipolar layer 3rd layer ganglion cells Fovea center of the retina concentration of cones Rods are present at every other spot peripheral retina besides the fovea Blind spot no receptors found in this spot optic nerve leaves the eye here brain assumes that the area around this is similar and thus fills in the blank are in your vision This is because the receptors are facing away from the light and the axons have to leave through the retina Photopigments light sensitive chemicals 1 protein transmembrane 1 vitamin retinal No light Na channels open membrane is depolarized release inhibitory neurotransmitter inhibits activity of bipolar and ganglion cells Light enzyme cascade light protein and lipid separate Na close membrane becomes hyperpolarized release of inhibitory neurotransmitter is reduced activity in bipolar cell is less inhibited firing rate of ganglion cell increases Photoreceptor to bipolar cell inhibitory connection Bipolar to ganglion cell excitatory connection Rods approx 120 million contain photopigment rhodopsin Very sensitive to light rods work best in dim light Detect different levels of light and dark not colors Most concentrated away from fovea Much larger receptive field can t see the details Cones approx 6 million contain photopigment iodopsin Requires high level of light work best in day light 3 kinds of iodopsin each reacts to different wavelengths One reacts more to shorter wavelengths blue React mostly to middle wavelengths green React mostly to longer wavelengths red Most concentrated in the fovea Porkengi shift can t see colors but blue colored surfaces look brighter than red colored surfaces because the response of the rods is shifted more towards the shorter wavelengths Almost a 1 1 ratio photoreceptor to ganglion cell Receptive field area of the retina from which a ganglion cell receives input