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Summary Sensation and Perception
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All senses, including sight, smell, hearing and touch receptors all explained with diagrams as reference
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Sensation and perception – Chapter 5Sensory receptors translate signals into nerve impulses – be it auditory signals from music, visual
stimuli like light, olfactory signals from smelling a fresh bakery, gustatory from eating the baked
goods, tactile from touching the baked goods, vestibular, proprioception and interoception –
SENSATION = detection of a stimuli by our sensory organs
We process new information sometimes by processing the current neural representation and
comparing it to previous knowledge. Helps us provide meanings to what we pick up through sensory
stimulation – PERCEPTION – organising the sensory information to give it a meaning.
Perception helps us differentiate between patterns that tell us two different things, so we must
contextualise what we see or hear or feel etc. This is either a B or a 13, depends on the
context.
Sensory processes
We are always bombarded by forces and radiation that we do not make a conscious effort to
perceive. We can barely even acknowledge their presence, for example, the radio signals to our
phones – perceiving and sensing so many stimuli would be confusing and overwhelming.
Sensory transduction: The characteristics of a stimuli are converted into nerve impulses
electromagnetic, chemical, forces etc.
Psychophysics: Relationship between sensory capabilities and physical stimuli
Vestibular system – ear has the cochlea associated with hearing, but also the vestibular system,
where our movements are respective to the world due to the direction of gravity being perceived.
Sensation of touch is more associated with the pressure on our external body or something we lay
our hands on purposefully.
Cutaneous: skin relations
When something passes through our stomach our when we feel our heartbeat against our chest, it is
the sense of interoception, where we understand our body’s internal movement.
Limits of sensitivity are the ranges of frequencies we can and cannot hear, the dimmest or brightest
of lights we can see etc.
Differences in limits are the smallest differences between two small ranges that dictates if we can
sense it, so 2 types of grey that we can see on a black screen, one we can, the other we cannot.
,Absolute threshold
Lowest intensity at which a stimulus can be detected 50% of the time. So, the lowest frequency
detectible by a subject, be it something that touches the skin or light shining through the eyes to
form an image.
Someone more sensitive can detect a stimulus at a low threshold value.
Absolute threshold varies over species.
So, for vision, the furthest away, generally speaking, a candle flame can be seen on a dark night is
50m, the tick of a watch can be heard at its quietest from around 20ft away (given there is no other
sounds) and one can smell a drop of perfume as it diffuses into a room.
Signal detection theory
Decision criterion: There cannot be a fixed value of detection, because certain
circumstances can enhance one’s sensation perception, so when someone watches a scary
movie, subtle sounds they would otherwise not hear can frighten them, thus there must be
some standard that a person is held to that then allows the stimulus detection to come
through, creating a range of intensities one can experience.
IF THE PHYSICAL DIFFERENCE CAUSES THE SUBJECT TO RESPOND DIFFERENTLY, SO BEING SCARED
MAKES THEM THINK THEY HEARD A WEIRD NOISE, THEN THE STIMULUS HAS BEEN DETECTED. BUT
IF THEY RESPOND THE SAME, SO THEY DO NOT PICK UP THE STIMULUS AS THEY HAVE NOT HAD A
CHANGE IN PHYSICAL STATE, THEN THEY DO NOT PICK UP THE STIMULUS.
Stimulus significance also enhances someone’s perception; you are likely not to respond to a
situation if you are not emotionally bothered by it.
Signal detection theory: People respond differently depending on the judgement factors involved; if
at war, and you hear a subtle footstep sound, you will respond to it, as a ‘miss’ can result in death if
something was potentially there. Others can use their equilibrium state to ignore stimulus, as they
do not have the haste or instinct to respond or heighten their senses should there be a response
to the stimulus due to any information that sheds light on the sensation or is there a lacking
information sector that does not allow a stimulus to be detected (you see a shadow more (stimulus)
when something you have seen in a film has scared you (information)).
, Always having a guard up and enhancing your sensation perception can cause paranoia and anxiety
that will not go away, thus having a naturally low absolute threshold frequency allows the subject to
remain calm and only sense something if they have the judgement factors there (they hear clear
footsteps etc.)
The difference threshold:
Smallest difference that can be detected between two stimuli 50% of the time – so something that
can just be noticed.
Weber’s law: the difference threshold is directly proportional to the magnitude of the stimulus from
which a comparison is derived. In simple terms, the stimulus intensity gets greater and more intense,
thus the difference between the stimulus sensations must be greater to then perceive the
difference.
So, for weight, if something is 50kg, you must deduce the next weight that then feels slightly
heavier; 50.2 would feel exactly the same, so when we use the Weber fraction for weight, we find
that 51kg can be sensed to be heavier. Compared to 500kg, the Weber fraction would mean the next
weight to be seen as heaver, must be 510kg, this difference being bigger than before and the
stimulus intensity of the weight being generally higher Weber weight fraction is n + 1/50
The lower the Weber fraction, the higher the sensitivity to the change/differences; when you slightly
salt something a bit more, you can taste this additional salt very clearly. Sound frequencies and
colour can get very difficult to perceive a difference between, as hue and tone can vary without
showing a vast change, until a very large difference is detected – some shades of black look the
same, but only when it is greyed to the point of turning grey, you notice the change in the shade.
Tonal pitch is the perception
of a sound wave subjective to
a person, so a low pith has a
low frequency, but the exact
sound and sensation differs
for people.
Injuries lead to inflammation or
can cause hot sweats, the worse
the injury, the stronger the
Loudness is determined by
reaction.
the amplitude of the wave,
not the frequency – frequency
is pitch.
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