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Sensation & Perception summary of chapters 1-7
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This document contains an elaborate summary of chapter 1 till 7 of the course Sensation & Perception at Utrecht University.
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SENSATION AND PERCEPTION LITERATURE PART 1CHAPTER 1 INTRODUCTION
Sensation: the ability to detect a stimulus and, perhaps, to turn that detection into a private experience.
Perception: The act of giving meaning to a detected sensation.
Methods used in the study of the senses:
1. Thresholds
2. Scaling – measuring private experience
a. Qualia: in reference to philosophy, private conscious experiences of sensation or perception.
3. Signal detection theory – measuring difficult decisions
4. Sensory neuroscience
5. Neuroimaging – an image of the mind
6. Computational models
Dualism: the idea that the mind has an existence separate from the material world of the body.
Materialism: the idea that the only thing that exists in matter, and that all things, including the mind and
consciousness, are the results of interaction between bits of matter.
Panpsychism: the idea that the mind exists as a property of all matter – that is, that all matter has
consciousness.
Psychophysics: the science of defining quantitative relationships between physical and psychological events.
Two-point touch threshold: the minimum distance at which two stimuli are perceptible as separate.
Just noticeable difference (JND)/ 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.
Weber fraction: the constant proportionality in Weber’s law.
Weber’s law: the principle describing the relationship between stimulus and resulting sensation that says he
the JND is a constant fraction of the comparison stimulus.
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.
Absolute threshold: the minimum amount of stimulation necessary for a person to detect a stimulus 50% of the
time.
Method of constant stimuli: a psychological method in which many stimuli, ranging from rarely to almost
always perceivable, are presented one at a time.
The multiple times piece is important here. You need to repeat the measure over and over and then average
the responses or otherwise describe the pattern of results.
A more efficient approach is the 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.
Method of adjustment: a method of limits in which the participant controls the change in the stimulus.
Moving beyond thresholds, suppose we wanted to know how strong your experiences are. Magnitude
estimates is a psychophysical method in which the participant assigns values according to perceives
magnitudes of the stimuli.
,Steven’s power law: a principle describing the relationship between stimulus and resulting sensation that says
the magnitude of subjective sensation is proportional to the stimulus magnitude raised to an exponent.
Comparisons:
1. Weber’s law involves a clear objective measurement. We know how much we varied the stimulus, and
either the observers can tell that the stimulus or they cannot.
2. Fechner’s law begins with the same sort of objective measurements as Weber’s, but the law is actually
a calculation based on some assumptions about how sensations works. Fechner’s law assumes that all
JNDs are perceptually equivalent. In fact, this assumption turns out sometimes to be incorrect and
leads to instances where the law is violated, such as in the electric shock example just given.
3. Steven’s power law describes rating data quite well, but notice that rating date are qualitatively
different from the data that support Weber’s law. We can record the observer’s ratings and we can
check whether those ratings are reasonable and consistent, but there is no way to know whether they
are objectively right or wrong.
Cross-modality matching: the ability to match the intensities of sensations that come from different sensory
modalities. This ability allows insight into sensory differences. This similarity between pitch and brightness
doesn’t count for taste
Signal detection theory: a psychophysical theory that quantifies the response of an observer to the
presentation of a signal in the presence of noise. Measures obtained from a series of presentations are
sensitivity and criterion of the observer. Many neurons in the brain are firing all the time, even when nothing is
happening. Signal detection theory exists to help us understand what’s going on when we make decisions
under conditions of uncertainty.
Criterion: in reference to signal detection theory, an internal threshold that is set by the observer. If the
internal response is above criterion, the observer gives one response, below criterion, the observer gives
another response. There are four possible outcomes:
- You might say no when there is no ringtone correct rejection/true negative
- You might say yes when there is a ringtone hit/true positive
- You might say yes when there is no ringtone false alarm/false positive
- You might say no when there is a ringtone miss/false negative.
Sensitivity: in reference to signal detection theory, a measure that defines the ease with which an observer can
tell the difference between the presence and absence of a stimulus or the difference between stimulus 1 and 2.
Receiver operating characteristic (ROC) curve: the graphical plot of the hit rate as a function of the false-alarm
rate. If these are the same, points fall on the diagonal, indicating that the observer cannot tell the difference
between the presence and absence of the signal. As the observer’s sensitivity increases, the curve bows
upward toward the upper left corner. That point represents a perfect ability to distinguish signal from noise.
The most powerful argument for a continuity between humans and animals came from Darwin’s theory of
evolution. An inescapable implication of the theory is that we can learn much about human sensation and
perception by studying the structure and function of our nonhuman relatives.
Doctrine of specific nerve energies: a doctrine, formulated by Johannes Müller, stating that the nature of a
sensation depends on which sensory fibres are stimulated, rather than how they are stimulated. The central
idea is that we cannot be directly aware of the world itself, but only of the activity in our nerves.
, The cranial nerves leading into the skull illustrate the doctrine of specific nerve energies. The cranial nerves
consists of 12 pairs of nerves, that originate in the brain stem and reach sense organs and muscles through
openings in the skull.
- Sensory information:
o Olfactory (I) nerves: the first pair of cranial nerves. The
axons bundle together after passing through the cribriform
plate to form the olfactory nerve, which conducts impulses
from the olfactory epithelia in the nose to the olfactory
bulb.
o Optic (II) nerves: arise from the retina and carry visual
information to the thalamus and other parts of the brain.
o Vestibulocochlear (VIII) nerves: connect the inner ear with
the brain, transmitting impulses concerned with hearing
and spatial orientation. Is composed of the cochlear nerve
branch and the vestibular nerve branch.
- Muscles that move the eyes:
o Oculomotor (III) nerves: innervate all the extrinsic muscles
of the eye except the lateral rectus and the superior oblique
muscles, and which innervate the elevator muscle of the
upper eyelid, the ciliary muscle. And the sphincter muscle of the pupil.
o Trochlear (IV) nerves: innervate the superior oblique muscles of the eye balls
o Abducens (VI) nerves: innervate the lateral rectus muscles of the eyeballs.
- Exclusively motor:
o Spinal accessory (XI)
o Hypoglossal (XIII)
- Both sensory and motor:
o Trigeminal (V)
o Facial (VIII)
o Glosspharyngeal (IX)
o Vagus (X)
Two specialized type of nerve cells are warmth fibres and cold fibres, which
respond to increases and decreases in temperature on the skin.
As processing extends beyond primary areas, cortex often becomes polysensory,
meaning that the information from more than one sense is being combined in
some manner.
(multi)sensory integration: the process of combining different sensory signals.
Some neurons increase the response of the next neuron (excitatory), whereas
other neurons decrease the response of the next neuron (inhibitory). It turned out that neurotransmitters
travel from the axon across the synapse to bind to receptor molecules on the dendrite of the next neuron.
Neuronal firing is actually electrochemical. Voltage increases along the axon are caused
by changes in the membrane that permit positively charged sodium ions to rush very
quickly into the axon from outside the cell. Then the membrane changes again in a way
that ushes positively charged potassium ions out of the axon, restoring the neuron to its
initial resting voltage.
One way to investigate what a neuron encodes is to try to
identify the stimulus that makes it fire the most vigorously.
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