Chapter 5 Sensation and Perception - Group 1

Sensation

Occurs when one of our senses (sight, smell, hearing, touch, or taste) is activated by something in our environment.
Occurs before the process of perception.
The process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment.

Sensory receptors

A sensory nerve ending that responds to a stimulus in the environment of an organism

Perception

The brains interpretation of sensory images.
Occurs after the process of sensation.
The process of understanding and interpreting sensory information, enabling us to recognize meaningful objects and events.

Transduction

The translation of incoming stimuli into neural signals (impulses) that our brain can interpret..
Neural impulses from the senses travel first to the thalamus and then onto different cortices of the brain.
The sense of smell is one exception to this rule.

Top-Down Processing

When we use this, we perceive the filling in gaps in what we sense.
Information processing guided by higher level mental processes, as when we construct perceptions drawing on our experience and expectations.
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 influence how we perceive the world.
Schemata can create a perceptual set, which is a predisposition to perceiving something in a certain way.

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.
Analysis that begins with the sensory receptors and works up to the brain's integration of sensory information.
We start our perception at the bottom with the individual characteristics of the image and put all of those characteristics together into our final perception. Our minds build the picture from bottom up using basic characteristics.

Pareidolia

Tendency to perceive meaningful images in meaningless stimuli, usually visual, so that one sees an object, pattern, or meaning where there is none.
The most common example are faces, likely due to the accessibility of schemata for faces and facial features. Other common examples are perceived images of animals or objects in cloud formations.
May extend to include hidden messages in recorded music played in reverse or at higher- or lower-than-normal speeds, and hearing voices (mainly indistinct) or music in random noise, such as that produced by air conditioners or fans.

Selective Attention

The focusing of conscious awareness on a particular stimulus

Cocktail-Party Phenomenon

If you are talking with a friend and someone across the room says your name, or something else of particular interest to you, your attention will probably involuntarily switch across the room.
An example of selective attention.

Inattentional Blindness/Change Blindness

Failing to see visible objects when our attention is directed elsewhere
Failing to notice changes in the environment is more specifically known as change blindness, a type of inattentional blindness.

Sensory Adaptation

Decreasing responsiveness to stimuli due to constant stimulation.
For example, we eventually stop receiving a persistent scent in a room.
This happens in your sensory organs.
Another example: You put a pen behind your ear and forget it is there after a while because you don't feel it anymore.

Sensory Habituation (also called Perceptual Adaptation)

Our perception of sensations as partially determined by how focused we are on them.
For example, no longer hearing traffic from the nearby freeway after having lived in a place for years.
While sensory adaptation happens in the sensory organs, sensory habituation happens in the brain. People who have habituated to something (e.g., a sound, a smell) can still perceive it if directed to focus attention on it. If you have adapted to it anymore, you can't perceive it (e.g. the cold of the water after you have been in the pool for a while).

Priming

The activation, often unconsciously, of certain associations, thus predisposing one's perception, memory, or response

Perceptual Set

A mental predisposition to perceive one thing and not another.
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 this predisposition to perceiving something in a certain way.
For example, you may perceive a cloud being shaped like a heart around Valentine's Day.

Absolute Threshold

The minimal amount of stimulus we can detect 50% 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.

Subliminal Messages

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

Signal Detection Theory

Investigates the effects of the distractions and inferences we perceive while experiencing the world.
Predicts how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise). Assumes there is no single absolute threshold and that detection depends partly on a person's experience, expectations, motvation, and alertness.
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 (such as not seeing a stop sign, or thinking that you see a friend in the distance when you are actually seeing a stranger).

Difference Threshold

Smallest amount of change (minimum amount of difference) needed in a stimulus before we detect a change 50% of the time..
Computed by Weber's law, named after psychophysicist Ernst Weber.
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.
If someone raises the volume on your phone and you notice the increase in volume, that increase in volume is above the difference threshold.
We experience this as a just noticeable difference (JND).

Weber's Law

The principle that, to be perceived as different, two stimuli must differ by a constant minimum percentage (rather than a constant amount).
Named after psychophysicist Ernst Weber.
Describes the difference thresholds 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.
For example, if you are playing very quiet music, you don't have to raise the volume much before someone notices. If the music is very loud, however, you have to raise the volume a lot before anyone will notice.

Extrasensory Perception (ESP)

The controversial claim that perception can occur apart from sensory input; includes telepathy (mind-to-mind communication), clairvoyance (perceiving remote events, such as a house on fire in another state), and precognition (perceiving future events, such as an unexpected death in the next month).
While perception is fed by sensation, cognition, and emotion, this claims that sensory input is not necessary.

Parapsychology

The study of paranormal phenomena, including ESP and psychokinesis/telekinesis (the supposed ability to move objects by mental effort alone)

Psychophysics

The study of relationships between the physical characteristics of stimuli, such as their intensity, and our psychological experience of them

Energy Senses

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

Chemical Senses

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

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 the eye through the cornea and pupil, is focused buy the lens, and is projected onto 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 from the left side of each retina (right vision field) go to the left hemisphere of the brain, and those from the right side of each retina (left vision 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.

Wavelength

The distance from the peak of one light or sound wave to the next.
Electromagnetic wavelengths vary from the short blips of gamma rays to the long pulses of radio transmission.

Hue

The dimension of color that is determined by the wavelength of light; what we know as the color names blue, green, and so forth

Visible Light

Color is perceived due to a combination of different factors:
Light intensity: how much energy the light contains determines how bright the object appears.
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).

Intensity

The amount of energy in a light or sound wave, which influences what we perceive as brightness or loudness, as determined by the wave's amplitude (height).

Visual Accommodation

The process by which the eye adjusts (by the lens changing shape) and is able to focus, producing a sharp image at various, changing distances from the object seen.

Occipital Lobe

Location of visual cortex.
Part of the brain that processes vision sensations.
-Receives impulses via in 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 hemisphere of the brain.

Feature Detectors

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

Parallel Processing

The processing of many aspects of a problem simultaneously; the brain's natural mode of information processing for many functions, including vision. Contrasts with the step-by-step (serial) processing of most computers and of conscious problem solving.

Color Blindness/Color Vision Deficiency

Individuals with dichromatic color blindness cannot see either red/green shades or blue/yellow shades.
Those who have monochromatic color blindness see only shades of gray.

Trichromatic Theory (Young-Helmholtz Theory)

A theory of color vision.
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.

Opponent-Process Theory

- A theory of color vision.
- States that the sensory receptors arranged in the retina come in pairs: red/green pairs, yellow/blue pairs, and black/white pairs.
- If one sensor is stimulated, its pair is inhibited from firing. This theory explains color afterimages.
- If you stare at the color red for a while, you fatigue the sensors for red. Then when you switch your gaze and look at the blank page, the opponent part of the pair for red will fire, and you will see a green afterimage.
- The Opponent-Process Theory explains afterimages and colorblindness.
- Most researchers agree that color vision is explained by a combination of the Trichromatic and Opponent-Process Theories.