Perception Flashcards
Definition of sensation
The registration of physical stimuli on sensory receptors
Definition of stimulus
An element of the world around us that impinges on our sensory systems
Definition of perception
The process of creating conscious perpetual experience from sensory input and acquisition of knowledge via the senses
What ways can we measure perception and how is it measured
Absolute Threshold- JND and Webers Law
Measure of limits, method of adjustment, staircase method, method of constant stimuli
What is meant by the absolute threshold
It is the smallest amount of stimulus energy necessary for an observer to detect a stimulus e.g. dimmest light needed
What is meant by JND
Just noticeable difference
smallest difference between 2 stimuli that a person can detect
What is tactile perception
perception that results from the mechanical deformation- indentation, vibration or stretching of the skin
Mechanoreceptors
Sensory receptors that transduce mechanical deformations of the skin into neural signals that are sent to the brain
What are SAI mechanoreceptors
Slow-adapting mechanoreceptors with merkel cell endings, have small receptive fields, dense on surface of skin
SAII mechanoreceptors
large receptive fields, sparse deep in skin
FAI mechanoreceptors
fast-adapting with meissner corpuscle endings, small receptive fields and densely arranged surface of skin
FAII mechanoreceptors
Fast-adapting with Pacinian corpuscle endings, large receptive fields and sparse deep in skin
What are FA good for?
suited for detecting vibration and motion
What are Merkel cells
Specialized endings of SAI mechanoreceptors where transduction takes place
What are meissner corpuscles
Specialized endings of FAI mechanoreceptors where transduction takes place
What are Pacinian corpuscles
Specialized endings of FAII where transduction takes place
Info on SAI
Merkel cell endings
Respond to spatial patterns on surfaces- bumps etc and braille
Assess the spatial resolution of tactile perception- two point threshold
Weinstein 1968- threshold is smallest (spatial resolution is greatest) on fingertips and lips and is much larger (lower resolution) on arms, legs and torso
what is two point threshold
used to assess spatial resolution of tactile perception
single pointed probe or pair of probes with small distance between them asking ppts to judge whether one or two locations are touched.
SAI mechanoreceptors studies Blake
Johnson & Lamb 1981
Monkeys- braille like patterns made using a rotating cylinder on fingertips
could show how the pattern of action potentials produced by an individual SAI fiber matched up with the entire pattern of the stimulus
Philips et al., 1990
Braille stimuli on human fingertips
compared using the three other types of mechanoreceptors not just SAI.
SAII and FAII provide no useful info on the patterns of stimuli
FAI fibers- blurry representations of the Braille patterns, much less precise than those produced by the SAI fibers.
Vega-Bermundez et al., 1991
compared behavioural responses people and monkeys
responses of monkey SAI fibers match up with patterns of error shown in confusion matrix.
Blake et al., 1997, Connor et al., 1990-
the difference in response rates of monkey SAI fibers to textures with different roughness almost perfectly matched the difference in human judgements about the roughness of the same textures.
khalsa et al., 1998
Although individual SAI fibers dont respond selectively to the orientation of edges pressed into the skin
SAI fibers provide reliable info about orientation
SAI fibers critically involved in identifying touched surfaces and objects
SAII info
Edin, 1992-
provide important info about skim stretch
perception of skin stretch plays a role in the perception of movement across the skin. Johnson, 2002- when you grasp an object and pick it up weight of object pulls the skin downward and provides feedback that lets you know whether the object is slipping from your grip
FAII info
Pacinian corpuscle endings
Very sensitive- good at perception of objects
judge roughness using a rigid probe (Klatzky & Lederman 1999)
Brisben et al., 1999- a vibration with an amplitude as little as 10 nanometers is sufficient enough to increase the firing rate of an FAII fiber
Pleasant Touch
C-tactile mechanoreceptors
unmyelinated mechanoreceptor and provides info about pleasant touch (Olausaaon et al., 2010)
free nerve endings only present in hairy skin
unmyelinated so carry signals slowly to the brain. - respond to slow, gentle touch sending signals to insular cortex
Ackerley et al., 2014-
after using a mechanical devise to stroke the forearm of ppts using varying speed and temperature
CT mechanoreceptors responded strongly to neutral temps and intermediate speeds, other mechanoreceptors firing rates increased when speed and temp increased.
suggest that speed and temperature important factors determining the strength of their response
Mechanoreceptor transduction
Kung 2005-
mechanical forces causes ion channels to open in the mechanoreceptor cell membrane
action potential
measured using cell membrane potential while directly applying mechanical forces to the cell (Hu & Lewin, 2006) amongst other techniques
Proprioception
perception of the position and movement of body parts, based on the information in neural signals from specialized sensors within those body parts.
Proske & Gandevia, 2009 note types of sensroy organs that provide info about joint angles.
MUSCLE SPINDLES- sensory organs that provide info about muscle length, isometric forces on muscles
GOLGI TENDON ORGANS- sensory organs that provide info about muscle force
JOINT RECEPTORS- provide info joint angle, to signal when a joint has reached its limit of its normal motion
Perceiving Pain
Yantis & Abrams
Pain- unpleasant sensory and emotional experience caused by potential or actual tissue damage
pain perception vital- Manfredi et al 1981 genetic disorder where someone can not perceive pain- dangerous
inflammatory pain-
pain that arises after tissue damage, chemical substances released by the damaged tissue either activate pain receptor or reduce threshold
Neuropathic pain-
caused by damage to the peripheral or central nervous system
Nociceptive pain-
arises from potential or actual tissue damage due to physical trauma
Nociception-
the perception of nociceptive pain
Affective perception- unpleasant physical or emotional experiences that motivates us to make the pain stop
Discriminative perception- allows us to determine where the pain is coming from, what it feels like and how intense it is
Nociceptors
Free nerve endings
transduce physical stimuli and transmit the neural signals associated with nociceptive and inflammatory pain
in dermis and epidermis
high threshold
Sensitization- decreases the response threshold of nociceptors so that even a very low stimulation of an injury site can cause pain
Transmit pain to spinal cord through A-delta fibers- myelinated axons. Rapid response
C-fibers- unmyelinated axons of nociceptors that transmit pain signals slowly
Thermoreception
Ability to sense the temperature of objects and surfaces in contact with the skin
THERMORECEPTORS- sensory receptors for the detection of temperatures within the range if about 17-43 degrees- free nerve endings in epidermis and dermis
WARM FIBERS- thermoreceptors that fire at an ongoing moderate rate in response to sustained skin temps on range 29-43
(Darian-Smith et al., 1973)
COLD FIBERS- fire at moderate rate in response to temps 17-40
(Darian-Smith et al., 1973)
maintain their increased firing rate for several seconds and then adapt to new temp and falls to baseline (Schepers & Ringkamp, 2009)
Pathways for receptors
DCML pathway
Dorsal column-medial lemniscal pathway
- pathway for signals involved in tactile perception and proprioception, travels up ipsilateral side, crosses to contralateral side in the medulla, through ventral posterior nucleus of thalamus and onto the somatosensory cortex
Spinothalamic pathway
-Signals for nociception and thermoreception, crosses to contralateral side within spinal cord and then through the ventral posterior nucleus of the thalamus and onto the cortex
VP nucleus
Ventral posterior nucleus
-a nucleus in the thalamus part of both the DCML pathway and the spinothalamic pathway
Somatosensory cortex
region of the cerebral cortex in the anterior parietal lobe, receives signals carrying sensory info via the ventral posterior nucleus of the thalamus
