Chapter 1 Introduction to Perception Flashcards
Describe allegory of a cave
The “Allegory of the Cave” is a scenario that says that our world is only made of what we are able to perceive. In this example, prisoners are in a dark cave. They are unable to move or see anything other than the shadows cast by objects and noises heard over a half wall made by a few guards in the cave. The shadows and noises comprise the entire world known by these prisoners, even if there are objects and noises beyond the cave exist.
As a result, we should not trust our senses because they cannot provide an accurate representation of our world
Explain the mechanism of adaptation and provide an example.
Our brains quickly adapt to things that do not change for a period of time. For example, when one enters a house and they may initially be bombarded with the smell of fresh cookies, however, once some time has passed the smell of fresh cookies will not be noticed anywhere.
What are sensory transducers and how are they related to perception?
Sensory transducers are receptors that convert physical energy from the environment into neural activity. According to Democritus, our perception is based on information passed through these receptors from the outside world.
What is nativism?
Nativism is the belief that the mind creates thoughts outside of external experiences. That we possess innate abilities that exist before we experience anything.
Explain why Descartes is known as a dualist.
Descartes is know as a dualist because he believes that our mind has an existence outside of the material world of the body.
Describe empiricism and provide an example of one empiricist.
Empiricism is the philosophy that we are only made of our experiences and what we perceive. Ad that this is the only source of knowledge. John Locke is an example of an empiricist.
Explain the notion of “tabula rasa.”
Tabula rasa is the belief that humans are born as a blank slate. We have no knowledge when we are brown. We must learn everything.
What is psychophysics?
Psychophysics is defined as the science of defining quantitative relationships between physical and psychological (subjective) events.
What is the “just noticeable difference” (JND)?
JND is the smallest detectable difference between two stimuli or the minimum change in a stimulus that enable it to be correctly judged as different from a reference stimulus.
Describe two psychophysical methods used to measure people’s sensations.
- ) Method of constant stimuli- a psychophysical method in which many stimuli, ranging from rarely to almost always perceivable (or rarely to almost always perceivably different from a reference stimulus) are presented one at a time. Participants respond to each presentation: “yes/no”’ “same/different” and so on.
- ) Method of Limits- A psychophysical method in which the particular dimension of a stimulus, or the difference between two stimuli is varied incrementally until the participant responds differently.
What is the method of adjustment?
–A method of limits in which the subject controls the change in the stimulus.
Explain Fechner’s law.
Fechner’s law describes the relationship between stimulus and resulting sensation that says the magnitude of subjective sensation increases proportionally to the logarithm of the stimulus intensity. S = k log R
Why is the JND important in psychophysics?
JND is important in psychophysics because JND provides a reliable way to quantify data in reference to sensations and perceptions.
What are the signal and noise in the signal detection theory?
The “signal” is the stimulus that one is trying to detect. The “noise” is the something that is always present, the background against which, we must detect the stimulus.
What is magnitude estimation?
Magnitude estimation is defined as a psychophysical method in which the participant assigns values according to perceived magnitudes of the stimuli.
What is the central idea of Müller’s doctrine of specific nerve energies?
States that the nature of a sensation depends on which sensory fibers are stimulated not on how fibers are stimulated.
What are cranial nerves?
Twelve pairs of nerves (one for each side of the body) that originate in the brain stem and reach sense organs and muscles through openings in the skull.
What is Helmholtz’s ophthalmoscope used for?
To view the retina
Explain how neurons communicate with one another
Neurons communicate with each other by releasing neurotransmitters. These neurotransmitters move from the axon, across the synapse, and to receptors on the dendrite of the next neuron.
What are neurotransmitters?
Neurotransmitters are a chemical substance used in neuronal communication a synapses.
When is an action potential created?
Action potential is created when the membrane of the neuron permits sodium ions to rush into the cell, thus increasing the voltage. then potassium ions flows out of the cell, bringing the voltage back to a resting rate. This process occurs along the length of the axon until the action potential reaches the axon terminal.
Overarching Principle of Perception
Perceptual systems evolve to obtain information about the environment that is relevant for the tasks the organism must perform in order to survive and reproduce.
Corollary: The design of a perceptual system is constrained by the tasks it performs, by the physical/statistical properties of the enviornment and various biological factors.
Five difficult problems for Vision Systems
Illumination Problem-The Illumination of scenes is highly variable and complex
Depth Problem
Images in the eyes are 2D projections of a 3D environment
Context Problem
Objects often appear in a complex and varying context of other objects
Viewpoint Problem
Objects are rarely seen from the same viewpoint.
Category complexity problem
The specific objects that define a category are often quite different
Fundamental biological constraints
Limited neural resources, dynamic ranges and physical spaces.
Recurrent Themes
Perception is a very complex process
Perception generally involves the integration of many sources of information most of which are not very reliable.
There are many approaches to the study of perceptual systems and each has made important contributions to our understanding.
Approaches to Understanding Perception
Natural Tasks Natural Scene Statistics Anatomy Responses of individual neurons Responses of neural populations Perceptual/behavioral performance Mathematical and computational modeling
Natural Tasks
Many of the major natural tasks involve natural sub-tasks. For example, image contours can occur for a number of entirely different physical reasons. They can be the result of surface boundaries, surface markings or shading. There can be little doubt that many perceptual tasks depend critically upon identifying whether a contour is a surface boundary, a marking or a shadow.
Natural Scene Statistics
- Characterize natural stimuli
- Identify sources of stimulus information available for performing natural tasks
- Determine how useful are those sources of stimulus information
- Generate hypothesis for how the brain might exploit the stimulus information
- Design experiments to test the hypothesized mechanisms
Two-Alternative Forced Choice Test
Example for an objective identification task with Feedback.
abducens (VI) nerves
The sixth pair of cranial nerves, which innervate the lateral rectus muscle of each eye.
absolute threshold
The minimum amount of stimulation necessary for a person to detect a stimulus 50% of the time.
auditory (VIII) nerves
The eighth pair of cranial nerves, which connect the inner ear with the brain, transmitting impulses concerned with hearing and spatial orientation. The auditory nerve is composed of the cochlear nerve branch and the vestibular nerve branch, leading to the alternate name vestibulocochlear nerve.
blood oxygen level–dependent (BOLD) signal
The ratio of oxygenated to deoxygenated hemoglobin that permits the localization of brain neurons that are most involved in a task.
computed tomography (CT)
An imaging technology that uses X-rays to create images of slices through volumes of material (e.g., the human body).
cranial nerves
Twelve pairs of nerves (one for each side of the body) that originate in the brain stem and reach sense organs and muscles through openings in the skull
criterion
In signal detection theory, an internal threshold that is set by the observer. If the internal response is above criterion, the observer gives one response (e.g., “yes, I hear that”). Below criterion, the observer gives another response (e.g., “no, I hear nothing”).
cross-modality matching
The ability to match the intensities of sensations that come from different sensory modalities. This ability enables insight into sensory differences. For example, a listener might adjust the brightness of a light until it matches the loudness of a tone.
cycles per degree
The number of pairs of dark and bright bars per degree of visual angle.
doctrine of specific nerve energies
A doctrine, formulated by Johannes Müller, stating that the nature of a sensation depends on which sensory fibers are stimulated, not on how fibers are stimulated.
dualism
The idea that the mind has an existence separate from the material world of the body.
electroencephalography (EEG)
A technique that, using many electrodes on the scalp, measures electrical activity from populations of many neurons in the brain.
event-related potential (ERP)
A measure of electrical activity from a subpopulation of neurons in response to particular stimuli that requires averaging many EEG recordings.
Fechner’s law
A principle describing the relationship between stimulus and resulting sensation that says the magnitude of subjective sensation increases proportionally to the logarithm of the stimulus intensity.
Fourier analysis
A mathematical procedure by which any signal can be separated into component sine waves at different frequencies. Combining these sine waves will reproduce the original signal.
functional magnetic resonance imaging (fMRI)
A variant of magnetic resonance imaging that makes it possible to measure localized patterns of activity in the brain. Activated neurons provoke increased blood flow, which can be quantified by measuring changes in of the response of oxygenated and deoxygenated blood to strong magnetic fields.
just noticeable difference (JND) (or difference threshold)
The smallest detectable difference between two stimuli, or the minimum change in a stimulus that enables it to be correctly judged as different from a reference stimulus.
magnetic resonance imaging (MRI)
An imaging technology that uses the responses of atoms to strong magnetic fields to form images of structures like the brain. The method can be adapted to measure activity in the brain, as well (see functional magnetic resonance imaging).
magnetoencephalography (MEG)
A technique, similar to electroencephalography, that measures changes in magnetic activity across populations of many neurons in the brain.
magnitude estimation
A psychophysical method in which the participant assigns values according to perceived magnitudes of the stimuli.
materialism
The idea that the only thing that exists is matter, and that all things, including the mind and consciousness, are the results of interaction between bits of matter.
method of adjustment
A method of limits in which the subject controls the change in the stimulus.
