Perception Flashcards
face pareidolia
tendency of visual system to see faces in inanimate objects
exteroception
information about external environment, involves the somatic nervous system
interoception
processing central information inside bodies, used to control motor output, involves autonomic nervous system
- afferent (sensory input)
- efferent (motor output)
reduced afferent sensory input:
continuous input is so important that individuals deprived of external stimulation become severely disoriented, vivid hallucinations and delusion, especially when deprivation is involuntary
generalised senses
sensory receptors scattered throughout the body, simple anatomical structures located in skin, muscles, joints and internal organs
specialised senses
sensory receptors localised within specialised organs in the head, complex anatomical structures
types of sensory receptors
mechanoreceptors - respond to movement and pressure, audition and touch
chemoreceptors - respond to airborne and soluble chemicals, smell and taste
photoreceptors - respond to visible light, vision
nocioceptors - respond to pressure, temperature, chemicals, somatic senses
thermoreceptors - respond to changes in temperature, chemical and mechanical stimuli through somatic senses, autonomic sensory pathways
stages of processing information
- Sensory receptors are stimulated by the appropriate environmental energy
- Sensory transduction: sensory receptors transduce (convert) physical energy into neural energy
- Sensory coding: resulting neural activity is encoded into patterns of neural activity and transmitted to and further processed in the CNS
- Neural processing in the cortex produces perception
absolute threshold
smallest amount of energy needed to detect a stimulus, not fixed, most physical intensities will be a mixture of supraliminal (perceived) and subliminal (not perceived) intensities
- the minimum amount of energy that can be detected 50% of the time
difference threshold
otherwise known as just noticeable difference
- the smallest detectable difference between stimuli
- smallest amount something has to change for a person to notice it 50% of the time
- therefore the more intense the stimulus, the larger the detectable difference must be
- used to show how what we percieve and what is in the physical environment differs
Weber’s Law
says the just noticeable distance is always a constant fraction of the stimulus intensity
- highlights the difference between physical and perceptual and dimensions, what physical instruments record and what we perceive are two different things
dynamic aspects of sensory processing
- response properties of our sensory and perceptual systems are not fixed
- the sensitivity of our sensory systems constantly change due to differing levels of stimulation and exposures to new physical environments
sensory adaptation
- A reduction in sensitivity to a stimulus after constant exposure to it
- It reduces our awareness of a constant stimulus and helps to free out attention and processing resources to other (novel) stimuli in our environment
- Present in all sensory modalities but much reduced in pain
rapidly adapting receptors (phasic) are:
most sensitive to changes in stimuli
slowly adapting receptors (tonic)
respond as long as the stimuli is applied
chemical senses
olfaction and gustation
olfaction
sensations evoked by airborne chemical compounds (odorants) that are able to stimulate olfactory receptors in the nose
- distance sense - provides information about chemicals suspended in the air around us
- strongly linked to emotional and memory processing
odorant (olfaction)
a molecule that is capable of stimulating olfactory receptors, require characteristics to stimulate sense of smell
- these include: volatility, hydrophobicity, small molecular weight
olfactory transduction
odorants enter the nasal cavity via a retronasal passage (nose or mouth)
- through the respiratory epithelium and olfactory epithelium
olfactory epithelium: site of olfactory transduction, converting physical energy to neural energy
- size is proportionate to the ability to smell, bigger epithelium the more sensitive the nose is
- located on roof of nasal cavity, where it traps odorants and connects them to receptors
- amount of olfactory receptors correlates to the sense of smell
respiratory epithelium: filter, humidify and warm the air we breath
transduction process for olfaction
dendrites of olfactory receptors activate in olfactory epithelium - sensory neurons activate in the olfactory bulb
Signals are sent to:
- The primary olfactory cortex (in cerebral cortex)
- Amygdala and limbic system (involved in emotional reactions to odours)
After primary olfactory cortex, it signals to second olfactory cortex (frontal lobe) and is integrated into other systems
Types of Sensory Coding in Olfaction
shaped-based coding, population coding, vibrational coding
Olfactory Sensitivity
- Early findings suggest that humans can discriminate between 100,000 different odours but latest estimates suggest differentiation between 1 trillion
- Detection sensitivity differs across different chemical compounds: some chemicals need lower concentration to be detected than other (lower absolute thresholds/better sensitivity)
Factors affecting sensitivity
- Women have lower thresholds
- Worst sensitivity in smokers and drinkers
- Better in the morning
- After 85, 50% unable to detect most smells
Recognition threshold, and olfactory example
level at which a stimulus can be recognised, labelled as something
- Generally, olfactory identification is poor, and cannot be determined with great accuracy
Porter (2007) - work on the ability to smell
humans can scent track, improve with practice, nostrils sample spatially distinct regions
pheromones
chemicals released by one animal detected by another that shape the second animal’s behaviour or physiology
- not clear role in humans (alteration of mood, menstrual synchrony)
major histocompatibility complex genes (MHC) and odour preference
preference for smells replicate a preference for genes that don’t match
- if the genes were to match their children would be less healthy (weaker immune systems), so their odour preference replicates gene compatibility
anosmia
inability to smell, most often resulting from various infections in the nasal cavity or head trauma
- rare - congenital
- profound loss of taste as well
- associated with decreased well-being and decrease quality of life
specific anosmia
the inability to smell one specific compound amid otherwise normal smell perception
gustation
sensations evoked by solutions in the mouth that contact receptors there
- receptors located on tongue and roof of mouth in clusters, in taste buds
- the distribution of receptor types on the tongue is even in humans
sensory coding of gustation
- simpler than olfaction
- labelled-line coding: modality specific receptors transfer the information through a line to higher levels of processing
- stimulus –> receptor –> perceived taste
taste central pathway
- signals from taste cells travel along various cranial nerves
- these pathways first synapse in the spinal cord and then the thalamus
- finally they terminate in the primary taste cortex and then project to the orbitofrontal cortex
taste threshold
minimal concentration of a substance detectable by taste
- people are most sensitive to bitter substances, higher preference for sweet and sour substances
genetic variations in bitter taste
Fox (1931) - certain bitter substances taste dramatically different to different people.
Gene for PTC/PROP
- Individuals with two recessive genes are nontasters
- Individuals with one or more of the genes are tasters
hypotaster, normal taster, super taster
hypotaster - indifferent or likes bitter, seeks spicy, adventurous eater
normal taster - tolerates bitter and spicy food, moderate
supertaster - avoids bitter and spicy food, picky eaters
somatic senses
touch, temperature, pain and proprioception
the components of the CNS and PNS that receive and interpret sensory information from the skin, joints, ligaments and muscles
skin senses - touch, pain, temperature
proprioception -
kinesthesia - the sense of position of our body parts with respect to each other that allows us to perform movement
vestibular sense - provides information about the position of body in space by sensing gravity, movement and acceleration (factors that are critical for maintaining our sense of balance)
Sensory Coding of Touch
- mechanoreceptors
Four different types of mechanoreceptors embedded in
- outer layer
- underlying layer of skin
- epidermis
- dermis
Each mechanoreceptor responds to a touch stimulus in a specific area of the skin (the receptive field of the receptor)
- All mechanoreceptors respond to touch but have different anatomy, adaptation rate and receptive field (RF) size
slow adapting mechanoreceptors
fire continuously as long as pressure is applied
primary functions
- fine detail (pattern, form perception)
- texture perception
- finger position
those with small RF sizes encode information from a smaller area of the skin than larger RF sizes
fast adapting mechanreceptors
fire at onset and offset of stimulation
primarily functions
- flutter
- vibration
- fine texture perception (moving fingers across something)
- stable grasp
Measuring Tactile Sensitivity and Acuity (3 ways)
absolute detection threshold –> finding the smallest pressure to be detected
two-pointed discrimination –> minimal distance between two points that can be detected, determining if your being touched by one needle or two needle
grating acuity –> distinguishing the minimal amplitude of grooves that can be discriminated to determine if something is a smooth and grooved surface
touch sensation
represented somatotopically in the brain
- Adjacent areas on skin connect to adjacent areas in the brain
- Certain body locations have a disproportionate amount of cortical area because of the increased sensitivity in those areas
phantom limb sensations (an example of neural plasticity)
- Feel limb sensations when amputated
- Result of cortical remapping that occurs in response to amputation: cortical regions that represent the lost limb before amputation can become responsive to stimuli from other adjacent cortical regions after the amputation
Encoding Temperature (through thermoreceptors)
→ types: warmth fibres, cold fibres
- Thermoreceptors respond when you make contact with an object warmer or colder than your skin
- Stimulating cold and warm fibres togethers produces a hot feeling (instead of the expected lukewarm)
Pain Perception
→ free nerve endings, source of information that relates to tissue destruction
→ pain perception is adaptive to a degree as it motivates behaviours to terminate the source of the pain
congenital analgesia
unable to feel pain
factors that lessen the experience of pain
- expectation, when told what to expect they feel less pain
- shifting attention, attention on stimuli other than the pain-inducing one lessens pain
- content of emotional distraction lessens pain to something else
Gate Control Theory (Melzak & Wall)
- theory that the spinal cord contains a neurological “gate” that blocks pain signals or allows them to pass on to the brain
- the gate can open by the activity of pain signals travelling up small nerve fibres
- the gate can close by activity in larger fibres or by information coming from the brain
Visual-Vestibular Sensory Integration
brain just using eyes and inner ear to coordinate eyes and head movement
examples of where it goes wrong
- vection - illusory sense of self motion produced when you are not moving
- motion sickness - results when there is a disagreement between the motion and orientation signals provided by the semicircular canals, otolith organs, and vision
audition
auditory perception is the ability to identify and localise the sound signals in environment
Sound is the periodic vibration of air molecules, originates from a disturbance of the air by any object, the local religion of air has increased energy caused by the motion of the air molecules
physical properties - amplitude
amplitude: determined by how much the sound source displaces the waves from the equilibrium
- Sound amplitude is the difference between the peak and the trough of a sound wave (spatial extent of pressure oscillations)
- measured in decibels
Decibel: the difference between two sounds as the ratio between two sound pressures
- Every increase of 10dB is equal to a 10-fold increase in sound pressure level
- 0dB, absolute threshold of hearing
physical properties - frequency
Determined by the rate of displacement caused by the sound source - how fast it reaches its displacement from the equilibrium
- The number of complete waveforms, or cycles, that pass a given point in space every second
- Measured in hertz (1hz is one cycle per second)
- Human range: 20-20,000 hz, infrasound and ultrasound are outside of hearing range
- All animals seem to have much wider hearing than voicing range
- Many animals have wider range of frequencies than is possible for humans
- Humans are most sensitive to sound frequencies between 1000-5000 hz (lowest auditory thresholds to these sounds)
physical properties - complexity
Combining multiple sound waves together makes it complex
- Sounds are typically more complex and contain energy at multiple frequencies
- Lowest frequency: fundamental frequency
- Integer multiples of lowest frequency are called harmonics
More complex = more frequencies
- Sounds complexity contributes to the perceptual quality of timbre
- Pitch of complex waves determined by fundamental frequency
perceived properties
loudness, pitch and timbre