Chapter 4 Sensation
The origins of knowlegde
Where does knowledge come from?
directly from the world around us.
from our ears, eyes, and other senses collecting what the world is providing
The passive perciever
John Locke: 17th century phiospher. argued that at birth, the human mind is much like blan tabet (a
Distal stimulus: an objec event in the outside world.
proximal stimulus: energies from the outside world that directly reach our sense organs.
visual perspective: a cue used to convey depth in many paintings.
the active perciever
person supplements the sensory imput with associations
percevier must categorize and interpret incoming sensory info
Immanuel Kant: german philosopher, 1724-1804,
argued that perception is possible only because the mind organizes the sensory info into certain
we have a grasp of certain spatial relationships.
o we understand what it means for one thing to be next to or far from another thing.
innate grasp of temopral relationships: for one thing to occur before or after, and what it means
for one event to cause another.
basic understanding of space, time, and causality brings order to our perception: without this
framework, Kant agrues that our sensory experience would be chaotic or meaningless.
psychophysic: an approach to perception that relates the characteristics of physical stimuli to the
sensory experiences they produce.
Sensory threshold absolute threshold: the smallest quantity of a stimulus that an individual can detect.
difference threshold: the smallest amount that given a stimulus must be increased or decreased so that
an individual can detect the difference.
just-noticeable difference JND: the smallest difference that an organism can reliably detect between two
Weber's Law: the observation that the size of the difference threshold is proportional to the intensity of
the standard stimulus.
Fechner's Law: the observation that the strenght of a sensation is proportional to the logarithm of
physical stimulus intensity.
Detection and decision
perceptual sensitivity: an organisms ability to detect a signal.
decision criteria: an organisms rule for how much evidence it needs before responding.
signal dection procedures
signal detection theory: the theory that percieving or not percieving a stimulus is actually a judgement
about whether a momentary sensory experience is due to the background noise alone or to the
background noise plus a signal.
payoff matrix: the pattern of benefits and costs associated with certain types of repsonses.
a survery of the senses
transduction: the process through which a physical stimulus is converted into a signal within the nervous
sensory coding: the process through which the nervous system represents the qualities of the incoming
stimulus, whether auditory or visual for examply or whether a red light or a green one a sour taste or a
psychological intensity: difference between a bright light and a dim one, or a subtle scent in contrast to
a dense cloud of smell.
sensory quality: how the nervous system represents the difference between vision and hearing. or
within a modality, how it represents the difference between a high pitched note and a low one
specificity theory: the proposal that different sensory qualities are signaled by different quality specific
neurons. this theory is only correct in a few cases. pattern theory: the proposal that different sensory qualities are encoded by specific patterns of firing
among the relevant neurons.
sensory adaptation: the process by which the sensivity to a stimulus declines if the stimulus is presented
for an extended period of time.
the vestibular sense
kinethesis: sensations generated by receptors in the muscles, tends, and joints that inform us of our
vestibular sense: sensations generated by receptors in the semicircular canals of the inner ear that
inform us about the heads orientation and movements.
skin senses: group of senses including pressure, warmth, cold and pain through which we gain info
about our immediate surroundings.
nociceptors: receptors in the skin that give rise to the sense of pain, they respond to various forms of
tissue damage and to temperature extremes.
gate control theory: the proposal that pain sensations must pass through a neural gate in order to reach
the brain and can be blocked at that gate by neurons that inhibit signals from the nociceptors.
olfactory epithelium: a mucous membran at the top of the nasal cavity,