I. Overview Sensation and Perception A. Sensation: awareness of simple characteristics B. Perception: making complex interpretations C. Top-Down vs Bottom-up Processing D. Psychophysics -- thresholds 1. example -- vision 2. example -- hearing
II. Sensation A. Only the sense organs (and their receptor cells) can respond directly to environmental stimuli 1. Specificity of each sense organ 2. Sense organs transduce (convert) physical energy from environment into neural activity B. If different kinds of stimulus energy is transduced into neural activity, how does the brain know what's what? 1. Anatomical specificity a. general location b. additionally, within region specificity 2. Temporal Coding - increase or decrease in rate of firing of neurons
III. Vision A. Characteristics of light 1. Visible light is part of a large spectrum of electromagnetic energy 2. Visible = ~400 & 700 nanometers 3. Physical stimulus attributes determine our perception: a. Frequency/wavelength determines hue (color) b. Intensity determines perceived brightness 1. not a linear relationship 2. logarithmic c. saturation (purity)
B. The Eye 1. Eye receptors respond to light energy 2. Structure a. Cornea b. Iris 1. circular band of muscles; colored; 2. controls amount of light entering pupil c. Lens: 1. adjusts so as to train the light rays --image--on the retina 2. fixation reflex
3. Near-sightedness or farsightedness 3. Receptor cells that make up retina a. Rods: don't perceive color 1. sensitive to low illumination 2. located in periphery of retina b. Cones: operate in greater illumination 1. sensitive to color differences, patterns 2. Fovea has only cones c. Blind spot: no rods or cones = no vision
4. Layers of retina a. Inside out & Upside down! 1. light passes through vitreous humor (fluid), ganglion cells and bipolar cells (transparent layers of neurons) to photoreceptors at the back of retina (rods and cones) b. Light energy (photons) causes chemical reactions with photopigments within the rods and cones 1. intensity is coded by rate of firing c. Rods and cones send graded potentials
1. to next layer: bipolar cells; also send graded potentials to 2. ganglion cells 3. action potentials then carried to the CNS by ganglion cells. d. Axons from the ganglion cells leave the eye through the optic nerve 1. pass through the thalamus 2. in route to the primary visual cortex in occipital lobe (Striate cx) 3. Visualize it e. 2 other kinds of cells in the retinal layer 1. horizontal cells 2. amacrine cells
5. Why all the different layers? a. To confuse and perplex students b. Data reduction c. Feature Detection C. Combining information in the brain 1. The visual pathways a. Main pathway: ganglion cells optic nerve optic chiasm thalamus striate cx b. Other pathways (do not memorize): 1. projections to hypothalamus 2. brainstem nuclei; control oculomotor system
3. brainstem areas; control pupil size control eye movements 4. Blindsight 2. Receptive fields 3. Multiple representations of images 4. Feature detectors: this is a model by Hubel & Wiesel a. Simple b. Complex c. Hypercomplex 5. Depth Perception a. Size cues b. Obstruction of some objects by others c. Binocular disparity
6. The human organism is designed to detect differences and change: a. brightness contrast b. lateral inhibition c. Contrast; microsaccades 7. Color vision is terribly complex a. Light is NOT colored -- our perception of it is b. In cones - 3 photopigments 1. Color blind persons have deficiency of one (or more) of the 3 photopigments 2. proportion of these 3 determines color 3. This does not explain everything -- e.g. how we see hybrid colors
c. Opponent-color process Theory (Hering) 1.. opponent colors -R+G, - B+Y and vice versa plus - Bl+W and vice versa 2. Vision takes place in two stages : trichromatic system, then opponent color system; After Images 8. Most of processing in Primary visual cortex is "non-color" a. Color processing seems to be added at a later stage b. processed and colorized info is still not recognizable as an object c. Where and What pathways d. Damage to these areas may result in agnosias D. Light/dark adaptation
1. How can we see across a wide range of light intensity? Two ways: a. existence of 2 kinds of receptors b. adaptation 2. Dark adaptation/ light adaptation a. light causes nerve impulse b. causes pigments to have a chemical reaction c. Pigments in cones vs rods d. In bright sunlight, there's a constant rate of splitting of rhodopsin (bleached out) e. When first in dark room, rhodopsin is depleted; needs time to reconstitute 3. Complete dark adaptation takes 30-45 mins
IV. Audition a. Rods & cones have different rate of dark adaptation b. Light adaptation much faster -- why? A. Characteristics of sound 1. frequency determines pitch a. humans range 20-20,000 Hz (cycles per second) b. other animals can hear much higher frequencies c. Most sounds are not pure 2. Amplitude determines loudness a. Sound measured in decibels (db's) b. logarithmic, not linear scale
B. The ear c. Humans have an immense range of intensities they can perceive 1. Outer ear 2. Auditory canal 3. Eardrum 4. Bones of middle ear a. hammer, anvil, stirrup b. transducing mechanism with 99.9% efficiency 5. Oval window 6. Cochlea (this is the place!!) 7. Semicircular (vestibular) canals C. The cochlea 1. Three fluid filled sections
2. Two membranes a. basilar vibrates b. preferential vibration for frequencies 3. Hair cells between two membranes are displaced as basilar membrane vibrates 4. Each hair cell gives one neuron in the auditory nerve D. So, how do we hear? 1. Duplex theory of pitch perception a. Place b. Vibration in synchrony with waveform 2. Sound localization -- DEMO! a. Arrival time differences for lower tones
b. Intensity differences for higher frequencies 3. The auditory system has excellent temporal resolution!