Measuring Perception Flashcards
Sensation
Detecting elementary properties of a stimulus; occurs at the beginning of a sensory system (e.g., light reaching the eye, sound waves entering the ear, food touching the tongue)
Perception
the experiences that result from complex processes that involve higher-order mechanisms such as interpretation and memory, which involve activity in the brain (e.g., identifying the food you are eating and remembering the last time you had it); giving meaning and/or purpose to the detected sensations
The perceptual process
- Stimulus in the environment
- Stimulus hits the receptors
- Receptor processes
- Neural processing
- Perception
- Recognition
- Action
Sometimes perception and recognition may happen in the same time or in reverse order
Distal stimulus
a stimulus that is out there in the environment (e.g., a tree)
Proximal stimulus
the representation of the distal stimulus that is relevant to the receptors (e.g., light reflected from the tree entering the eye and reaching the visual receptors)
Principle of representation
everything a person perceives is not based on direct contact with stimuli but on representations of stimuli that are formed on the receptors and the resulting activity in the nervous system, e.g., the image of the stimulus on the receptors represents the tree in the person’s eyes
Principle of transformation
stimuli and responses created by stimuli are transformed between the distal stimulus and perception, e.g., the first transformation is the reflection of light by the tree. the next one is the transformation of the reflected light that reaches the eye to neural signals
Sensory receptors
cells specialized to respond to environmental energy. They perform transduction - the transformation of environmental energy into electrical energy. Each sensory system’s receptors respond to a specific type of energy.
Processing process
The electrical signals that are produced by transduction travel through a network of neurons towards and within the brain. During the trip, the signals are processed (changed). As a result of this, some signals are reduced/prevented from reaching the brain, while others are amplified.
Primary receiving area
the region of the cerebral cortex to which the transduced signals are often sent. after reaching the primary receiving area, signals are then transmitted to many other structures in the brain
behavior (step 5)
the electrical signals have been transformed into the conscious experience of perception
recognition (step 6)
placing an object in a category that gives it meaning
Visual form agnosia
inability to recognize an object when visually perceiving it, despite correctly recognizing its parts
Bottom-up (data-based) processing
processing that is based on the stimuli reaching the receptors
top-down (knowledge-based processing)
processing that is based on previous knowledge about how things usually appear in the environment. Previous knowledge can influence perception, especially the process of categorization. this happens more often when the stimulus is complex. The person is usually unaware of this influence.
Psychophysics
measures the relationships between the physical (the stimulus) and the psychological (the behavioral response)
the oblique effect
people see horizontal/vertical lines better than lines oriented obliquely (at any orientation other than horizontal/vertical)
grating acuity
the smallest width of lines that subjects can detect
the stimulus-physiology relationship
the oblique effect can also be measured by measuing brain activity (physiological variable) in response to the grating stimuli. Studies show larger brain responses in visual brain areas for hoizontal/vertical orientations compared to oblique orientations
the physiology-behavior relationship
an experiment for the oblique effect that discovers a physiology-behavior relationship would measure both brain activity and behavior and compute the strength of the relationship between them
Proprioception
awareness of the location of our body parts
How many senses do we have?
more than 5: there are many senses providing us with information about the inner state of our bodies (hunger, thirst, inner body pain, etc.)
Absolute threshold
the minimum intensity of a stimulus that can be detected. In the grating acuity example, the absolute threshold was the smallest line width that could be detected.
Method of limits
the experimenter presents stimuli in either ascending order (intensity is increased) or descending order (intensity is decreased)
Crossover point
the point where the stimulus becomes (un)detectable. It usually varies in different trials (in ascending trials it takes more intensity to report detection and in descending trials it takes more decreases in intensity to report non-detection), which is why the procedure is repeated a number of times and then the results are averaged
Method of constant stimuli
similar to the method of limits, except that the stimuli are presented in a random order, each stimulus being presented many times. The absolute threshold is usually defined as the intensity that results in detection on 50% of trials.
Method of constant stimuli - advantage
most accurate, because crossover effects from different trials are minimized
Method of constant stimuli - disadvantage
time-consuming because it requires many observations to be done to find a crossover point reliably.
-> due to variability in the nervous system, stimuli near the threshold will be detected sometimes and missed at other times
Method of adjustment
the participant adjusts the stimulus until he/she can just barely detect it. The procedure is repeated multiple times and the absolute threshold is determined by averaging the thresholds in the different trials
-> fastet method
magnitude estimation
the experimenter presents a baseline stimulus to the participant (e.g., a sound of moderate intensity) and assings it a numeric value (e.g., 10). Then more sounds of different intensities are presented, and the participant assigns a number to their perceived loudness. This number is the perceived magnitude of the stimulus.
recognition testing
asking people to name objects or pictures of objects in order to test their ability to recognize (categorize) the stimuli
phenomenological report
asking a person to describe in their own words what they perceive (e.g., in the Rorschach test).
Cross-modality matching
an observer adjusts a stimulus of one sort to match the perceived magnitude of a stimulus of a completely different sort (e.g, adjust the brightness of a light until it matches the loudness of a particular tone).
Signal detection theory
assumes that all perceptual decisions must be made against a background of noise generated in the world or in the nervous system
Signal
the stimulus that a subject tries to detect. the signal is always surrounded by noise. when trying to detect a low-intensity signal, a subject has to do it in the presence of internal (fluctuations in the nervous system) and external noise (in the environment)
criterion
an internal threshold that determines the response to a perceptual task, e.g., detecting a phone ring while showering (in the presence of water noise). if the internal response is above the criterion, the subject gives a positive response. otherwise, the subject gives a negative response.
Correct rejection
saying “no” when there is no signal
hit
saying “yes” when there is a signal
false alarm
saying “yes” when there is no signal
miss
saying “no” when there is a signal
sensitivity
the ratio of hits to false alarms. denoted by d’
Sensory code
the way environmental stimuli are represented in the nervous system
specificity coding
the idea that a neuron can represent only one stimulus (e.g., a face). This idea is old and not accepted by neuroscientists today.
Sparse coding
the idea that a particular stimulus is represented by a pattern of firing of a small group of neurons, with the majority of neurons remaining silent. There is evidence for sparse coding in the visual, auditory and olfactory systems
Population coding
the idea that a particular stimulus is represented by a pattern of firing of a large number of neurons. There is evidence for population coding in the each of the senses, and for cognitive functions
Difference threshold
the smallest difference between 2 stimuli that enables us to tell the difference between them. Also called the just noticeable difference (JND).
Weber’s law
Weber observed that the JND when comparing a standard stimulus to a varying stimulus is a constant fraction of the standard stimulus.
the smallest change in weight: 1/40 of the standard weight
smalles change in line length: 1/100
Weber fractions
the constants (e.g. 1/40, 1/100) in Weber’s law
Fechner’s law
S = k x logR, describes the relation between a stimulus and the resulting psychological sensation
S = psychological sensation
R = physical stimulus level
k = constant
therefore, our psychological experience of the intensity of a stimulus increases less quickly than the actual physical stimulus increases
Steven’s power law
S = a x l^b
describes the same relationship as Fechner’s law:
S = psychological sensation
l = physical stimulus intensity
b = a constant exponent
a = a constant that corrects for the used units
Fechner’s and Weber’s laws both predict that a sensation always grows less rapidly than the stimulus. this does not always agree with Steven’s power law
psychometric function
a mathematical function that models the relationship between a given feature of a physical stimulus and the responses of a human/animal test subject
