AP Psychology: Sensation and Perception

Trichromatic Theory

- A theory of color vision (the other theory is Opponent-Process Theory). - Hypothesizes that we have three types of cones in the retina: cones that detect the primary colors of light- blue, red, and green. - These cones are activated in different combinations to produce all the colors of the visible spectrum. - Even though this theory has some research support and makes sense intuitively, it cannot explain such visual phenomena as afterimages and color blindness. - Most researchers agree that color vision is explained by a combination of the Trichromatic and Opponent-Process Theories.

Sensation

- Activation of our senses (sight, smell, hearing, touch, taste). - Occurs before the process of perception (the brain interpreting these sensations).

Visible Light

- Color is perceived due to a combination of different factors: 1. Light intensity - How much energy the light contains determines how bright the object appears. 2. Light wavelength - The length of the light waves determines the particular hue we see. We see different wavelengths within the visible light spectrum as different colors.

Sensory Adaptation

- Decreasing responsiveness to stimuli due to constant stimulation. - For example, we eventually stop perceiving a persistent scent in a room.

Gestalt Rules

- Developed by a group of researchers from the early 20th century who described the principles that govern how we perceive groups of objects (e.g., proximity, similarity, continuity, closure). - Based on observation that we normally perceive images as groups, not as isolated elements. - This process believed to be innate and inevitable.

Vision

- Dominant sense in human beings. Sighted people use vision to gather information about their environment more than any other sense. - The process of vision involves several steps: 1. Light is reflected off objects. 2. Reflected light coming from the object enters eye though the cornea and pupil, is focused y the lens, and is projected on to the retina where specialized neurons are activated by the different wavelengths of light. 3. Transduction occurs when light activates the special neurons in the retina and sends impulses along the optic nerve to the occipital lobe of the brain. 4. Impulses form the left side of each retina (right visual field) go to the left hemisphere of the brain, and those from the right side of each retina (left visual field) go to the right side of the brain. 5. Visual cortex receives the impulses from the retina, which activate feature detectors for vertical lines, curves, motion, among others. What we perceive visually is a combination of these features.

Constancy

- Every object we changes minutely from moment to moment due to our changing angle of vision, variations in light, and so on. - Our ability to maintain a constant perception of an object despite these changes. - Several types of constancy: size constancy, shape constancy, and brightness constancy.

Gate-Control Theory

- Explains how we experience pain. - Some pain messages have a higher priority than others. When a high-priority message is sent, the gate swings open for it and shut for low-priority messages, which will not be felt. - Of course, this gate is not a physical gate swinging in the nerve, it is just a convenient way to understand how pain messages are sent. For example, when you scratch an inch, the gate swings open for you high-intensity scratching and shuts for the low-intensity itching; this stops the itching for a short period of time. - Endorphins, or pain-killing chemicals in the body, also swing the gate shut. Natural endorphins in the brain, which are chemically similar to opiates like morphine, control pain.

Lens

- Focuses light that enters the pupil - Curved and flexible in order to focus the light. - As the light passes through the lens, the image is flipped upside down and inverted. - The focused inverted image projects on the retina.

Kinesthetic Sense

- Gives us feedback about the position and orientation of specific body parts. - Receptors in our muscles and joints send information to our brain about our limbs. - This information, combined with visual feedback, lets us keep track of our body.

Cocktail-party Phenomenon

- If you are talking with a friend and someone across the room says your name, your attention will probably involuntarily switch across the room. - An example of sensory habituation and selective attention.

Fovea

- Indentation at the center of the retina where cones are concentrated. - When light is focused onto your fovea, you see it in color. - Your peripheral vision, especially at the extremes , relies on rods and is mostly in black and white.

Retina

- Like a screen on the back of your eye. - As the light passes through the lens, the image is flipped upside down and projected on the retina. - Special neurons in the retina (cones, which detect color, and rods, which detect black and white) are activated by light and send impulses along the optic nerve to the occipital lobe of the brain.

Smell

- Molecules of substances rise into the air and are drawn into our nose. - The molecules settle in a mucous membrane at the top of each nostril and are adsorbed by receptor cells located there. - As many as 100 different types of smell receptors may exist. These receptor cells are linked to the olfactory bulb, which gathers the messages form the olfactory receptor cells and sends this information to the brain. - Nerve fibers from the olfactory bulb connect to the brain at the amygdala and then to the hippocampus, which make up the limbic system, which is responsible for emotional impulses and memory. - This direct connection to the limbic system may explain why smell is such a powerful trigger for memories.

Weber's Law

- Named after psychophysicist Ernst Weber. - Describes the difference threshold for different senses. - The change needed is proportional to the original intensity of the stimulus. The more intense the stimulus is, the more it will need to change before we notice a difference.

Optic Nerve

- Nerve leading from the retina that carries impulses to the occipital lobe of the brain. - The optic nerve is divided into two parts. Impulses form the left side of each retina (right visual field) go to the left hemisphere of the brain, and those from the right side of each retina (left visual field) go to the right side of the brain.

Taste (Gustation)

- Nerves involved in the chemical senses (taste and smell) respond to chemicals rather than to energy. - Taste buds on the tongue absorb chemicals from the food we eat. - Taste buds are located on papillae, the bumps you can see on your tongue. Taste buds are located all over the tongue and on some parts of the inside of the cheeks and roof o the mouth. - Humans sense four different types of tastes: sweet, salty, sour, and bitter. - People differ in their ability to taste food. The more densely packed the taste buds, the more chemicals are absorbed, and the more intensely the food is tasted. - The flavor of food is actually a combination of taste and smell.

Size Constancy

- Objects closer to our eyes will produce bigger images on our retinas but we take distance into account in our estimations of size. - We keep a constant size in mind for an object (if we are familiar with the typical size of the object) and know that it does not grow or shrink in size as it moves closer or farther away.

Shape Constancy

- Objects viewed from different angles will produce different shapes on our retinas, but we know the shape of an object remains constant. - For example, the top of a coffee mug viewed from a certain angle will produce an elliptical image on our retinas, but we know the top is circular due to shape constancy.

Pupil

- Opening in the center of the eye. - Similar to the shutter of a camera - Muscles that control the pupil (called the iris) open it (dilate) to let more light in and also make it smaller to let less light in.

Bottom-up Processing

- Opposite of top-down processing. - Instead of using our experience to perceive an object, we use only the features of the object itself to build a complete perception. - We start our perception at the bottom with the individual characteristics of the image and put all those characteristics together into our final perception. Our minds build the picture from the bottom up using basic characteristics.

Perceptual Set

- Our experience creates schemata, mental representations of how we expect the world to be. Our schemata influence how we perceive the world. - Schemata can create a perceptual set, which is a predisposition to perceiving something in a certain way.

Sensory Habituation

- Our perception of sensations is partially determined by how focuses we are on them. - For example, no longer hearing traffic from the nearby freeway after having lived in a place for years.

Occipital Lobe

- Part of the brain that processes vision sensations. - Receives impulses via the optic nerve. - The optic nerve is divided into two parts. Impulses from the left side of each retina (right visual field) go to the left hemisphere of the brain, and those from the right side of each retina (left visual field) go to the right side of the brain.

Feature Detectors

- Perception researches Hubel and Weisel discovered that groups of neurons in the visual cortex respond to different types of visual images. - Visual cortex has feature detectors for vertical lines, curves, and motion, among others. What we perceive visually is a combination of these features.

Cornea

- Protective covering on the front of the eye - Helps focus the light

Depth Cues

- Researchers divide the cues that we we use to perceive depth into two categories: 1. Monocular cues - Depth cues that do not depend on having two eyes (e.g., linear perspective, interposition, shading, and texture gradient). 2. Binocular cues - Cues that depend on having two eyes (e.g., retinal disparity and convergence).

Touch

- Sense of touch is activated when our skin is indented, pierced or experiences a change in temperature. - Some nerve endings in the skin respond to pressure; others respond to temperature. - Brain interprets the amount of indentation (or temperature change) as the intensity of the touch, from a light touch to a hard blow. - We sense placement of the touch by the place on our body where the nerve endings fire. - Nerve endings are more concentrated in different parts of our body. If we want to feel something, we usually use our fingertip, an area of high nerve concentration, rather than the back of our elbow, an area of low nerve concentration. - Pain is a useful response because it warns us of potential dangers.

Difference Threshold

- Smallest amount of change needed in a stimulus before we detect a change. - Computed by Weber's law, named after psychophysicist Ernst Weber.

Absolute Threshold

- Smallest amount of stimulus we can perceive. - Technical definition - the minimal amount of stimulus we can detect 50 percent of the time. - For example, the absolute threshold for vision is the smallest amount of light we can detect, which is estimated to be a single candle flame about 30 miles (48 km) away on a perfectly dark night.

Rods and Cones

- Special neurons in the retina that are activated by light. - Cones are activated by color. - Rods respond to black and white.

Subliminal Messages

- Stimuli below our absolute threshold - Research does not support claim that subliminal messages affect our behaviors in overt ways.

Perception

- The brain's interpretation of sensory messages. - Occurs after the process of sensation (the activation of our senses of sight, smell, hearing, touch, and taste). - The process of understanding and interpreting sensations.

Hearing

- The hearing process occurs in several steps: 1. Sound waves, vibration in the air, travel through the air, and are then collected by our ears. 2. Sound waves have amplitude and frequency. 3. Amplitude is the height of the wave and determines the loudness of the sound, which is measured in decibels. 4. Frequency, which is measured in megahertz, refers to the length of the waves and determines pitch. 5. Vibration s enter the ear and vibrate the eardrum, which connects with three bones in the middle ear: the hammer (or malleus), the anvil (or incus), and the stirrup (or stapes). 6. The vibration is transferred to the oval window, a membrane very similar to the eardrum. 7. The oval window membrane is attached to the cochlea, where the process of transduction occurs and neural messages are sent to he auditory cortex in the temporal lobe.

Cochlea

- The process of transduction (where sound waves are changed into neural impulses) occurs in the cochlea. - Shaped like a snail's shell and filled with fluid. As sound waves move the fluid, hair cells move. Neurons are activated by movement of the hair cells. - Neural messages are sent to the auditory cortex in the temporal lobe.

Chemical Senses

- The senses of taste and smell. - These senses work by gathering chemicals

Energy Senses

- The senses of vision, hearing, and touch. - These senses gather energy in the form of light, sound waves, and pressures, respectively.

Blind Spot

- The spot on the retina where the optic nerve leaves the retina and there are no rods or cones. - We cannot detect objects in our blond spot, but our brains and the movement of our eyes accommodate for the blind spot, so we usually don't' notice it.

Pitch Theories

- Theories that explain how we hear different pitches or tones. - Place Theory explains that the hair cell sin the cochlea respond to different frequencies of sound bases o where they are located in the cochlea. - According to Frequency Theory, Place Theory accurately describes how hair cells sens the upper range of pitches but not the lower tones. Lower tones are sensed by the rate at which the cells fire. We sense pitch because the hair cells fire at different rates (frequencies) in the cochlea.

Signal Detection Theory

- Theory that takes into account how motivated we are to detect certain stimuli and what we expect to perceive. These factors together are called response criteria. - By using factors like response criteria, Signal Detection Theory tries to explain and predict the different perceptual mistakes we make.

Sound Waves

- Vibrations in the air. They travel through the air and are collected by our ears. - Sound waves have amplitude and frequency. - Amplitude is the height of the wave and determines the loudness of the sound, which is measured in decibels. - Frequency, which is measured in megahertz, refers to the length of the waves and determines pitch.

Brightness Constancy

- We perceive objects as being a constant color even as the light reflecting off the object changes. - For example, we will perceive a brik wall as brick red even as the daylight fades and the actual color reflected form the wall turns gray.

Top-down Processing

- When we use top-down processing, we perceive by filling in gaps in what we sense. - Occurs when you use your background knowledge to fill in gaps in what you perceive. - Our experience creates schemata, mental representations of how we expect the world to be. Our schemata, mental representations of how we expect the world to be. Our schemata influence how we perceive the world. - Schemata can create a perceptual set, which is a predisposition to perceiving something in a certain way.