Sensation and Perception 5

Questions to Consider: I. How Do We Sense Our Worlds? II. What Are the Basic Sensory Processes? III. What Are the Basic Perceptual Processes?

I. How Do We Sense Our Worlds? Stimuli Must Be Coded to Be Understood by the Brain Psychophysics Relates Stimulus to Response

I. How Do We Sense Our Worlds? Sensation is our sense organs’ detection and responses to external stimulus energy Perception is the brain’s processing of detected signals that results in internal representations of stimuli

1. Stimuli Must Be Coded to Be Understood by the Brain Sensory Coding Transduction Process through which stimuli reaching the receptors are converted to neural impulses

2. Psychophysics Relates Stimulus to Response By studying how people respond to different sensory levels, scientists can determine thresholds and perceived change Absolute threshold: minimum intensity of stimulation that must occur before experiencing a sensation

2. Psychophysics Relates Stimulus to Response Difference threshold (DT): minimum amount of change required for a person to detect a change or difference between stimuli Ex. 1oz2oz=easy to detect difference (DT low) 5lb5lb 1oz=harder to detect (DT high)

2. Psychophysics Relates Stimulus to Response Our sensory systems are tuned to both adapt to constant levels of stimulation and detect changes in our environment Signal detection theory: detecting a stimulus involves making a judgment about its presence or absence based on a subjective interpretation of ambiguous information

2. Psychophysics Relates Stimulus to Response Sensory adaptation: decrease in sensitivity to a constant level of stimulation Ex. Perfume/cologne, strong when you put it on but intensity wears off in a few minutes, because it is continuous

II. What Are the Basic Sensory Processes? In Taste, Taste Buds Detect Chemicals In Smell, the Nasal Cavity Gathers Odorants In Touch, Sensors in the Skin Detect Pressure, Temperature, and Pain In Hearing, the Ear Detects Sound Waves In Vision, the Eye Detects Light Waves Humans and Animals Have Other Sensory Systems The Evidence for Extrasensory Perception (ESP) Is Weak or Nonexistent

1. In Taste, Taste Buds Detect Chemicals Gustatory sense (gustation): sense of taste Evolved to detect poisons Taste buds: sensory receptors that transduce taste information

1. In Taste, Taste Buds Detect Chemicals Uses taste buds to respond to the chemical substances that produce at least five basic sensations: sweet, sour, salty, bitter, and umami (savory) The number and distribution of taste buds vary among individuals Supertasters test (pg188) Cultural taste preferences begin in the womb

2. In Smell, the Nasal Cavity Gathers Odorants Olfaction: sense of smell, when receptors in the nose respond to chemicals. Olfactory epithelium (thin layer of tissue embedded with smell receptors) Receptors respond to chemicals and send signals to the olfactory bulb, in the brain The brain center for smell (just under the frontal lobes)

2. In Smell, the Nasal Cavity Gathers Odorants Females are much more accurate than males at detecting and identifying odors Scientists have devised various theories to explain this sex difference Decrease in sense of smell early indicator of Alzheimer’s

3. In Touch, Sensors in the Skin Detect Pressure, Temperature, and Pain Haptic sense : sense of touch Temperature, pressure, pain, sense of limbs in space Relies on tactile stimulation to activate receptors for temperature, for sharp and dull pain, and for other sensations

3. In Touch, Sensors in the Skin Detect Pressure, Temperature, and Pain Gate control theory Neural “gates” in the spinal cord also control pain We can reduce pain perception by: Distraction, visualizing pain as more pleasant, being rested and relaxed, learning how to change brain activity that underlies pain perception, and taking drugs that interfere with the neural transmission of pain or render us unconscious

4. In Hearing, the Ear Detects Sound Waves Audition: sense of sound The size and shape of sound waves (pattern of changes in air pressure) activate different hair cells in the inner ear The receptors’ responses depend on the sound waves’ frequency and timing and on the activated receptors’ location along the basilar membrane

4. In Hearing, the Ear Detects Sound Waves Self hearing test (pg198) Having two ears allows us to locate the source of a sound

5. In Vision, the Eye Detects Light Waves Light enters through the cornea, thick clear covering of the outer eye Focuses light = refraction Light passes through the lens, further refraction The pupil, black circle in the center of the eye, contracts or dilates to control amount of light that enters eye The iris, colored, circular muscles of the eye that control the contraction and dilation of the pupil An image is focused on the retina, thin inner surface on the back of the eyeball, contain photoreceptors (rods and cones)

5. In Vision, the Eye Detects Light Waves Rods: retinal cells responsible are for low levels of light and result in black and white perception (night vision) Cones: retinal cells that respond to higher levels of light and result in color perception

5. In Vision, the Eye Detects Light Waves Transmission from the eye to the brain Ganglion cells send signals along their axons from inside the eye to the thalamus Optic nerve carries information to the central nervous system (blind spot pg202) Optic chiasm: splits information from right eye to left hemisphere and vice versa Visual information transmitted to the primary visual cortex

5. In Vision, the Eye Detects Light Waves Detection of visual information: Sensory neurons respond to particular “tunings” Respond best to particular colors, shapes, etc. Receptive field Population of sensory receptors that influences activity in a sensory neuron

(a) A typical receptive field consists of a center and a surround (a) A typical receptive field consists of a center and a surround. When there is no light, the cell fires at its baseline rate. (b) When light is shined in the center, the neural firing frequency increases. (c) When light is shined in the surround, the neural firing frequency decreases. (d) When light is shined in the center and in the surround, the cell’s firing rate is balanced out and is similar to its baseline rate.

5. In Vision, the Eye Detects Light Waves Lateral inhibition: Visual systems are sensitive to edges If a rod or cone is stimulated, it sends information to its neighboring receptors, inhibiting their activity

5. In Vision, the Eye Detects Light Waves Color is determined by wavelengths of light, which activate certain types of cones; by the absorption of wavelengths by objects; or by the mixing of wavelengths of light

5. In Vision, the Eye Detects Light Waves Color mixing Subtractive color mixing means the mixture occurs within the stimulus and is a physical process Paint mixing Additive color mixing occurs when lights of different wavelengths are mixed, psychological process Stage lighting

6. Humans and Animals Have Other Sensory Systems In addition to the five “basic” senses, humans and other animals have: Kinesthetic sense Ability to judge where one’s limbs are in space Vestibular sense Ability to compare one’s bodily position to the upright position

7. The Evidence for Extrasensory Perception Is Weak or Nonexistent Little or no good evidence supports the intriguing idea that some people have additional sensory systems that allow them to know what other people are thinking, for example, or to predict the future

III. What Are the Basic Perceptual Processes? Perception Occurs in the Brain Object Perception Requires Construction Depth Perception Is Important for Locating Objects Size Perception Depends on Distance Perception

1. Perception Occurs in the Brain Neural activity in the primary auditory cortex gives rise to hearing In the temporal lobe Codes for frequency (pitch) Touch is mediated by neural activity in the primary somatosensory cortex In the parietal lobe More sensitive area=more cortical space Ex. Face and hands

1. Perception Occurs in the Brain Vision results from a complex series of events in various areas of the brain but primarily in the occipital lobe

These are the primary sense areas where information about taste, touch, hearing, smell, and vision are projected. Note that separate “streams” of visual information—what you see and where it is—are sent from the occipital lobe (visual cortex) to different parts of the brain for further processing.

1. Perception Occurs in the Brain What versus where: Neurons in different parts of the brain tend to have different receptive fields Ventral stream: what pathway (colors, shapes) Dorsal stream: where pathway (spatial perception)

2. Object Perception Requires Construction The Gestalt principles of stimulus organization account for some of the brain’s perceptions of the world Those perceptions involve cues about similarity, proximity, form, figure and background properties, and shading

Gestalt psychology describes how perceived features of a visual scene are grouped into organized wholes.

2. Object Perception Requires Construction Face perception: Faces are so important that certain brain regions appear to be dedicated to perceiving them Fusiform gyrus People recognize angry facial expressions more quickly than happy ones People are better at recognizing members of their own race or ethnicity, or sex

3. Depth Perception Is Important for Locating Objects Binocular depth perception: An object’s pattern of stimulation on each of the two retinas informs the brain about depth Monocular depth perception: Pictorial cues use information from the object’s appearance relative to the surroundings to perceive depth and relative motion

4. Size Perception Depends on Distance Perception Illusions of size can be created when the retinal size conflicts with the known size of objects in the visual field, as in the Ames illusions

Ames played with depth cues to create size illusions Ames played with depth cues to create size illusions. For example, as illustrated here, he made a diagonally cut room appear rectangular by using crooked windows and floor tiles. When one child stands in a near corner and another (of similar height) stands in a far corner, the room creates the illusion that they are equidistant from the viewer; therefore, the closer child looks like a giant compared to the child farther away.