Chapter Six: Vision Assorted Materials from Modules 1-3 Chapter Seven: Audition Module 1

1. Chapter Six: VisionAssorted Materials from Modules 1-3Chapter Seven: AuditionModule 1

2. Visual Coding and Retinal Receptors Reception- absorption of physical energy (electromagnetic waves) by receptors Transduction-the conversion of physical energy to an electrochemical pattern in the neurons Coding- one-to-one correspondence between some aspect of the physical stimulus and some aspect of the nervous system activity

3. Visual Coding and Retinal Receptors From Neuronal Activity to Perception coding of visual information in the brain does not duplicate the stimulus being viewed General Principles of Sensory Coding Muller and the law of specific energies-any activity by a particular nerve always conveys the same kind of information to the brain Now close your lid and poke your eye� do you see light (fosphenes)(sp?) Qualifications of the Law of Specific Energies the rate of firing or pattern of firing may signal independent stimuli timing of action potentials may signal important information indicating such things as movement the meaning of one neuron depends on what other neurons are active at the same time

4. Visual Coding and Retinal Receptors-�Look into My Eyes!� The Eye and Its Connections to the Brain Pupil-opening in the center of the eye that allows light to pass through Lens-focuses the light on the retina Retina-back surface of the eye that contains the photoreceptors The Fovea-point of central focus on the retina The Route Within the Retina photoreceptors-rods and cones bipolar cells-receive input from rods and cones ganglion cells-receive input from bipolar cells optic nerve-made up of axons of ganglion cells blind spot-the point where the optic nerve leaves the eye

9. Visual Receptors: Rods and Cones, Reception & Transduction continued Rods -abundant in the periphery of the retina -best for low light conditions -see black/white and shades of gray Cones abundant around fovea best for bright light conditions see color Table 6.1 is very good

10. Transduction Both Rods and Cones contain photopigments (chemicals that release energy when struck by light) 11-cis-retinal is transformed into all-trans-retinal in light conditions this results in hyperpolarization of the photoreceptor the normal message from the photoreceptor is inhibitory Light inhibits the inhibitory photoreceptors and results in depolarization of bipolar and ganglion cells

11. Theories Color VisionThe Trichromatic (Young-Helmholtz) Theory KEY POINT: We perceive color through the relative rates of response by three kind of cones, each kind maximally sensitive to a different set of wavelengths, but receptors are not equally distributed across retina. (exercises)

12. More Theories of Color Vision

14. Neural Basis of Visual Perception An Overview of the Mammalian Visual System Rods and Cones synapse to amacrine cells and bipolar cells Bipolar cells synapse to horizontal cells and ganglion cells Axons of the ganglion cells leave the back of the eye The inside half of the axons of each eye cross over in the optic chiasm Pass through the lateral geniculate nucleus Transferred to visual areas of cerebral cortex The visual pathway: Light rays reflected by an object--for example, a pencil--enter the eye and pass through its lens. The lens projects an inverted image of the pencil onto the retina at the back of the eye. Signals produced by rod and cone cells in the retina then start on their way into the brain through the optic nerve and reach a major relay station, the LGN (lateral geniculate nucleus). Signals about particular elements of the pencil then travel to selected areas of the primary visual cortex, or V1, which curves around a deep fissure at the back of the brain. From there, signals fan out to "higher" areas of cortex that process more global aspects of the pencil such as its shape, color, or motion. Surprisingly, light rays must penetrate two layers of neurons in the retina before reaching the precious rods and cones at the back: a middle layer of bipolar cells, and a front layer of ganglion cells whose long axons (fibers that transmit electrical impulses to other neurons) form the optic nerve leading into the brain. The visual pathway: Light rays reflected by an object--for example, a pencil--enter the eye and pass through its lens. The lens projects an inverted image of the pencil onto the retina at the back of the eye. Signals produced by rod and cone cells in the retina then start on their way into the brain through the optic nerve and reach a major relay station, the LGN (lateral geniculate nucleus). Signals about particular elements of the pencil then travel to selected areas of the primary visual cortex, or V1, which curves around a deep fissure at the back of the brain. From there, signals fan out to "higher" areas of cortex that process more global aspects of the pencil such as its shape, color, or motion. Surprisingly, light rays must penetrate two layers of neurons in the retina before reaching the precious rods and cones at the back: a middle layer of bipolar cells, and a front layer of ganglion cells whose long axons (fibers that transmit electrical impulses to other neurons) form the optic nerve leading into the brain.

15. Neural Basis of Visual Perception Concurrent Pathways in the Visual System In the Retina and Lateral Geniculate Two categories of Ganglion cells Parvocellular-smaller cell bodies and small receptive fields, located near fovea; detect visual details, color Magnocellular-larger cell bodies and receptive fields, distributed fairly evenly throughout retina; respond to moving stimuli and patterns In the Cerebral Cortex V1-Primary Visual Cortex-responsible for first stage visual processing V2-Secondary Visual Cortex-conducts a second stage of visual processing and transmits the information to additional areas Ventral stream-visual paths in the temporal cortex Dorsal stream-visual path in the parietal cortex

17. Neural Basis of Visual Perception- The Cerebral Cortex: The Shape Pathway Hubel and Wiesel�s Cell Types in the Primary Visual Cortex Simple Cells has fixed excitatory and inhibitory zones in its receptive field Complex Cells receptive fields cannot be mapped into fixed excitatory and inhibitory zones Respond to a pattern of light in a particular orientation

18. Neural Basis of Visual Perception- The Columnar Organization of the Visual Cortex Columns are grouped together by function Ex: cell within a given column respond best to lines of a single orientation Are Visual Cortex Cells Feature Detectors? Feature Detectors-neurons whose responses indicate the presence of a particular feature Shape Analysis Beyond Areas V1 and V2 Inferior Temporal Cortex (V3)-detailed information about stimulus shape (V4)-Color Constancy; Visual Attention (V5)-Speed and Direction of Movement

19. Neural Basis of Perceptual Disorder Disorders of Object Recognition Visual Agnosia-Inability to Recognize Objects Prosopagnosia-Inability to recognize faces Color Vision Deficiencies Complete and Partial Color Blindness-inability to perceive color differences Generally results from people lacking different subsets of cones genetic contributions- same photopigment made on medium and longwave wavelength receptors

20. Neural Basis of Visual Perception-The Cerebral Cortex The Cerebral Cortex: The Color Pathway Parvocellular to V1 (blobs) to V2, V4, and Posterior Inferior Temporal Cortex The Cerebral Cortex: The Motion and Depth Pathways Structures Important for Motion Perception Middle-temporal cortex-V5-speed and direction of movement Motion Blindness-Inability to detect objects are moving

21. Experience and Visual Development Early Lack of Stimulation of One Eye-blindness occurs in that one eye Early Lack of Stimulation of Both Eyes-if this occurs over a long period of time, loss of sharp receptive fields is noted Restoration of Response and Early Deprivation of Vision-deprive stimulation of the previously active eye and new connections will be made with the inactive eye Uncorrelated Stimulation in Both Eyes-each cortical neuron becomes responsive to the axons from just one eye and not the other

22. Experience and Visual Development Early Exposure to a Limited Array of Patterns�most of the neurons in the cortex become responsive only to the patterns that the subject has been exposed to Lack of Seeing Objects in Motion-become permanently disable at perceiving motion Effects of Blindness on the Cortex-parts of the visual cortex become more responsive to auditory and tactile stimulation

23. Chapter SevenThe Nonvisual Sensory Systems- Auditory SystemModule One

24. Audition Sound and the Ear Physical and Psychological Dimensions of Sound Amplitude=intensity of wave=loudness frequency=number of waves/second=pitch

25. Anatomy of the Ear Structures of the Ear Pinna-cartilage attached to the side of the head Tympanic Membrane-eardrum middle ear bones-hammer/anvil/stirrup oval window-membrane leading to inner ear cochlea-three fluid-filled tunnels scala vestibuli scala media scala tympani basilar membrane-flexible membrane tectorial membrane-rigid membrane hair cells-auditory receptors

26. Pitch Perception Theories of Pitch Perception Frequency theory- the basilar membrane vibrates in synchrony with a sound, causing auditory nerve axons to produce action potentials at the same frequency Place theory- the basilar membrane resembles the strings of a piano in that each area along the membrane is tuned to a specific frequency and vibrates whenever that frequency is present Volley principle- the auditory nerve as a whole can have volleys of impulses up to about 5,000 per second, even though no individual axon can approach that frequency by itself

29. Pitch Perception in the Cerebral Cortex Primary auditory cortex Each cell responds best to one tone Cells preferring a given tone cluster together Secondary auditory cortex Each cell responds to a complex combination of sounds

31. Hearing Loss Conductive Deafness bones of the middle ear fail caused by tumors, infection, disease usually corrected by surgery or hearing aids Nerve Deafness damage to cochlea, hair cells or auditory nerve usually treated with hearing aids caused by genetics, disease, ototoxic drugs, etc.

32. Localization of Sound Sound Shadow-loudest in nearest ear Time of arrival-arrives at one ear soonest Phase difference-sounds arrive out of phase dependent on frequency