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SENSATION & PERCEPTION. CHAPTERS 4 & 5 AP PSYCHOLOGY. SENSATION. How do we take in information?. A sense is a system that translates information from outside the nervous system into neural activity. Messages from senses are called sensations
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SENSATION & PERCEPTION CHAPTERS 4 & 5 AP PSYCHOLOGY
How do we take in information? • A sense is a system that translates information from outside the nervous system into neural activity. • Messages from senses are called sensations • For example, vision is the system through which the eyes convert light into neural activity. This tells the brain something about the source of the light (brightness) or about the objects from which the light is reflected (round, red, etc).
Elements of a Sensory System • Energy (light, sound waves, etc) contains info about the world • Accessory Structures (lens, ear, etc) modify energy. • Transduction- the process of converting incoming energy into neural activity through sensory receptors • Sensory nerves transfer the coded activity to the Central Nervous System. • Thalamus processes and relays the neural response (except in smell). • Cortex receives input and produces the sensation and perception
How does physical energy get converted into neural activity? CODING - translation of the physical properties of a stimulus into a pattern of neural activity that specifically identifies those physical properties. Doctrine of Specific Nerve Energies - stimulation of a particular sensory nerve provides codes for that one sense, no matter how the stimulation takes place Temporal Code - involves changes in the timing of the neurons firing. Ex: A bright light will cause some neurons in the visual system to fire faster than a dim light. Spatial Code - the location of the firing neurons provides information about the stimulus (tells us where the sensation is coming from).
HEARING • Sound is a repetitive fluctuation in the pressure of a medium, such as air. • In a place like the moon, which has almost no atmospheric medium, sound cannot exist • When you speak, your vocal cords vibrate, producing fluctuations in air pressure that spread as waves. A wave is a repetitive variation in pressure that spreads out in 3 dimensions.
Physical Characteristics of Sound • Amplitude- (intensity) difference in air pressure from the baseline to the peak of a wave. • Wavelength- the distance from one peak wave to the next. • Frequency- number of complete waves, or cycles, that pass by a given point in space every second. Described in a unit called hertz, (Hz). 1 cycle per second is 1 hertz
Psychological Dimensions of SoundWhat do we actually hear? • Loudness- determined by amplitude. Greater amplitude = Louder sounds • Pitch- how high or low a tone sounds. Determined by frequency. • High frequency = High Pitch • Low Frequency = Low Pitch • Timbre- (pronounced “tamber”) is the quality of the sound
The Ear • Auditory accessory structures modify sound waves before information affects neural signals • Pinna – crumpled part of ear that funnels sound through the ear canal • Tympanic Membrane – eardrum – tightly stretched membrane in the middle ear where sound waves strike • Vibrations of the tympanic membrane are transferred through 3 tiny bones - malleus (hammer), incus (anvil), stapes (stirrup) Sound Waves 1
Auditory Transduction • After sound passes through the oval window, it enters the inner ear or cochlea - this is where transduction occurs • The basilar membrane forms the floor of this long tube • Sound waves bend hairs of the organ of Corti – a group of cells which rest on the membrane • Hair cells connect with fibers from the auditory nerve, a bundle of axons that goes into the brain Sound Waves 2 Figure 4.4: The Cochlea
Auditory Pathways • Auditory nerve brainstem thalamus • The information coded in the activity of auditory nerve fibers is conveyed to the brain and processed further • Information is relayed from the auditory nerve to an area of the cerebral cortex called the primary auditory cortex • Various aspects of sound processed in different regions of auditory system. • Certain parts of auditory cortex process certain types of sounds.
How we hear? • http://www.youtube.com/watch?v=CSO765hyxrc&feature=related
Sensing Pitch • Different people may experience the “same” sound as different pitches. • Pitch-recognition abilities influenced by genetics. • Cultural factors are also partly responsible for the way in which a pitch is sensed.
Locating Sounds • Determined partly by the very slight difference in when sound arrives at each ear. • The brain also uses information about the difference in sound intensity at each ear.
Coding Intensity and Frequency • The more intense the sound, the more rapid the firing of a given neuron. • Frequency appears to be coded in two ways: place theory and frequency-matching theory
Coding Frequency: Place Theory • Sounds produce waves that move down the basilar membrane. • Where the wave peaks depends on the frequency of the sound. • Hair cells at a particular place on the membrane respond most to a particular frequency.
Coding Frequency: Frequency Matching Theory • Firing rate of an auditory nerve matches a sound wave’s frequency. • Sometimes called the “volley theory” of frequency coding.
Vision • Light – electromagnetic radiation • Visible light has a wavelength from just under 400 nanometers to 750 nanometers • Light intensity – • How much energy the light contains • Determines the brightness of light • Light Wavelength – • The difference between peaks in light waves • Determines what color we see
Great amplitude (bright colors, loud sounds) Short wavelength=high frequency (bluish colors, high-pitched sounds) Long wavelength=low frequency (reddish colors, low-pitched sounds) Small amplitude (dull colors, soft sounds) Physical Properties of Light Waves
Accessory Structures of the Eye • Cornea – curved, transparent layer through which light rays enter the eye • Pupil – opening in the eye through which light passes • Iris – colorful part of the eye which adjusts the amount of light entering the eye • Lens – bends rays, focusing them on the retina • Retina – Surfaces at back of the eye onto which the lens focuses light rays
Vision • Accommodation- the process by which the eye’s lens changes shape to help focus near or far objects on the retina • Acuity- the sharpness of vision • Nearsightedness- condition in which nearby objects are seen more clearly than distant objects because distant objects in front of retina • Farsightedness- condition in which faraway objects are seen more clearly than near objects because the image of near objects is focused behind retina
How Light enters the eye • http://www.youtube.com/watch?v=15P8q35vNHw
Vision Normal Vision Nearsighted Farsighted
Converting Light into Images • Visual transduction is the conversion of light energy into neural activity. • Conversion done by photoreceptors in the retina. • Two main types of photoreceptors: Rods and cones.
Rods and Cones • Rods • peripheral retina • detect black, white and gray • twilight or low light • Cones • near center of retina • fine detail and color vision • daylight or well-lit conditions
Interactions in the Retina • Photoreceptor cells connect to bipolar cells and then to ganglion cells • Axons of the ganglion cells form the optic nerve, which extends out of the eye and into the brain • Each neuron of a sensory system has a receptive field – part of the retina and the region of the environment to which that cell responds
Figure 4.11: Center-Surround Receptive Fields of Ganglion Cells
Figure 4.12: The Hermann Grid The cell whose receptive field includes the space at the intersection has more whiteness shining on its inhibitory surround than the cell whose receptive field is just to the right of the intersection. The output of the intersection cell will be lower than that of the one on the right, creating the impression of a shadow.
Visual Pathways • Axons from ganglion cells converge as a bundle of fibers called the optic nerve and exit the eyeball at one spot • The exit point has no photoreceptors and is insensitive to light creating a blind spot • About ½ the fibers of the optic nerve cross over to the opposite side of the brain at the optic chiasm (part of the bottom surface of the brain)
Visual Pathways con’t • Axons from most of ganglion cells in retina form synapses in the thalamus, in a specific region called the lateral geniculate nucleus (LGN) • Neurons in the LGN relay the visual input to the primary visual cortex, located in the occipital lobes in the back of the brain
Visual Representations • Receptive fields of neurons are characterized by parallel processing and hierarchical processing • Parallel Processing of visual properties: Brain conducts separate kinds of analysis simultaneously on the same information. • The “what” system • The “where” system • Hierarchical Processing of visual properties: • Individual cells in the visual cortex receive input from several LGN neurons. • Cortical cells respond to specific features of objects in the visual field – Feature detectors Light Conversion
Seeing Color • Hue – color determined by the dominant wavelength in the mixture of the light (excludes black, white, gray) • Saturation – purity of a color • Brightness – overall intensity of the wavelengths that make up light
Visual Information Processing • Trichromatic (three color) Theory • Young and Helmholtz • three different retinal color receptors
Trichromatic Theory of Color • Any color can be produced by mixing pure lights of blue, green, and red. • There are three types of cones, each most sensitive to particular wavelengths. • Ratio of the activities of the three types of cones indicates what color is sensed.
Opponent-Process Theory • Ewald Hering • Each of the three color sensitive elements are organized as pairs, where each pair member opposes, or inhibits, the other • Red-Green • Blue-Yellow • Black-White
The Chemical Senses • Olfaction detects airborne chemicals • Our sense of smell • Gustation detects chemicals in solution that come into contact with receptors inside the mouth • Our sense of taste
Olfactory System • Employs about 1,000 different types of receptors. • Only sense that does not send its messages through the thalamus. • Processing in several brain regions including frontal lobe and amygdala • Strong relationship between olfaction and emotional memory
Olfactory System (cont’d.) • Only sense that does not send its messages through the thalamus. • Pathways from olfactory bulb sends information on for further processing in several brain regions. • Including frontal lobe and amygdala. • Strong relationship between olfaction and emotional memory.
