Week 5: Sensation & Perception Flashcards
Sensation & Perception
Sensation describes the physical effects of an environmental stimulus on our nervous system.
Perception describes the psychological effects that the environmental stimulation has on us.
Sensory transduction: conversion of physical energy into neural activity
Specialised sense organs and sensory receptors
Sensory transduction is performed by a special class of cells called “sensory receptors”.
(1) vision, (2) hearing, (3) taste and smell, (4) touch and pain, and (5) balance.
Anatomy of the eye
- The cornea sits at the front of the eye and is involved in bending light from the environment into the eye.
- Behind the cornea is a space filled with a jelly-like substance called the aqueous humor.
- Behind the aqueous humor you will find the iris, the pupil, and the lens.
- The role of the pupil is to allow light to enter the inside of your eyeball – called the posterior chamber – so it can be detected by the receptor cells within the eye.
- The posterior chamber is also filled with a jelly-like substance, called the vitreous humor.
- The specialised receptor cells are found in the black layer of cells at the back of the eyeball, called the retina. - - - The retina is where the specialised receptor cells – called rods and cons.
Cones and Rods
Cones are involved in the detection of colour. There are three types of cones, which are maximally sensitive to detecting the colours blue, green or red.
Rods are sensitive to changes in light.
Sensory transduction in the visual system
- Light is focused by the cornea, enters the eye through the pupil, and is focused again by the lens to cast a clear and focused image of objects in the world onto the retina at the back of the eye.
- Light reaching the rods and cones is transduced into neural activity, which ultimately ends up affecting the activity of retinal ganglion cells.
- The axons of ganglion cells in the retina carry visual information from each eye to the brain by way of the optic nerve.
(The role of the optic nerve is to transmit the visual information which is collected from the eyeball to the brain for processing.)
Perception of depth clues
Monocular depth cues
Relative motion (or motion parallax): objects which are very far away appearing to move very slowly, whereas the objects closer to us appearing to move past us much more quickly.
Occlusion: refers to whether one object partially or fully blocks the view of another object.
Binocular cues: Convergence and divergence and Binocular disparity
Perception of motion clues
- Neurons in visual cortex, called motion detectors, that only respond when they detect something is moving in a particular direction and at a particular speed.
- Phi phenomenon occurs when two separate images are alternated on-and-off in quick succession, we will perceive the illusion of motion between the two images.
Amplitude and Frequency
Amplitude corresponds to the intensity of a sound.
The frequency of the sound is measured in cycles per second. This is measured in Hertz (Hz) and corresponds to perceived tone or pitch of a sound.
Anatomy of the human ear
The “fleshy” structures we have on the side of our heads are called the pinnae are the outermost section of the ear. This outer layer of the ear plays a role in directing vibrational energies from the environment into our middle ear, so that the vibrations can be transduced into auditory information by the structures of the inner ear.
Transductions of vibrations to sounds
Sound waves are focused via the pinnae of the outer ear into the ear canal, causing the eardrum to vibrate.
Three delicate interconnected bones of the middle ear amplify the vibrations of the eardrum to compensate for the large loss of mechanical energy.
The cochlea of the inner ear receives the vibrational/mechanical energy in the form of push-pull pulsations from the stirrups of the middle ear onto the oval window of the cochlea.
The vibrational energy passes down along the cochlea in the form of oscillations of the basilar membrane and tectorial membrane, which sit one above the other within the cochlea.
It is inside the cochlea where vibrational energy is transduced into a neural signal which can be processed by the auditory system into sounds. The transduction of vibrations to sounds occurs through specialised sensory receptors called hair cells.
The hair cells’ electrochemical signals result in impulses being sent along axons – collectively referred to as the auditory nerve – to the brain.
How do we perceive pitch and location?
Location: ‘binaural’ neurons allow us to compare the sound coming from the two ears.
Pitch:
- According to the frequency theory, the frequency of oscillation of the basilar membrane corresponds to the frequency of the original sound source.
- The volley principle, a group of hair cells, each sampling the sound intermittently and then combining their efforts can sufficiently ‘capture’ information about a wider range of vibrational frequencies.
- According to place theory, the base of the basilar membrane is stiffer than the apex of the basilar membrane.
Chemoreceptors
The specialised receptor cells which transduce chemicals into “tastes” and “smells”
Taste and the gustatory system process
When an object enters your mouth, molecules from the object will become dissolved into our saliva, and the saliva will carry these dissolved molecules to the taste receptor cells to be transduced into a “taste”.
These gustatory receptor cells are organized into barrel-shaped structures which somewhat resemble flower buds, called our taste buds.
Each taste bud is embedded in the tongue and contains a small opening at the top called the taste pore. Each taste pore is a fluid-filled funnel into which the finger-like extensions of the underlying taste receptor cell extend into. It is here where the receptors of the gustatory system are exposed to the dissolved chemicals in the saliva, and sensory transduction occurs.
The chemoreceptors inside our taste buds transduce the molecules within the saliva into neural signals, which are then sent via afferent nerve fibres through the brain stem and thalamus, to the gustatory cortex located in the frontal lobe.
Smell and the olfactory system process
- Two olfactory bulbs extend directly from the brain, one into each nasal cavity.
- Olfactory receptor cells represent the extensions of the olfactory nerves into the olfactory membrane of each bulb.
- At the end of each olfactory receptor cell are numerous tendrils that possess the receptor sites which airborne molecules can bind to, potentially triggering a neural impulse in the receptor cell.
- The neural signals transduced by our olfactory receptor cells send this information via the olfactory tract directly to the olfactory cortex, located in the temporal lobe.
How do we perceive “touch” sensory information
Specialised mechanoreceptor systems called proprioceptors within the muscles, tendons and joints that respond to the position, movement, and strain experienced by body parts.
