Sensation And Perception Flashcards
Sensation vs perception
Sensation is the awareness resulting from the stimulation of a sense organ (the physical effects of an environmental stimulus on our nervous system)
Perception is the organisation and interpretation of sensations (the psychological effects that the environmental stimulus has on us)
Sensory transduction
Is the process in which physical energy from the environment is converted into neural activity which can be interpreted by the nervous system
Specialised sense organise and sensory receptors
Sensory transductions is performed by a special class of cells called sensory receptors. These receptors have dendrites which have been fundamentally modified to make them highly and selectively responsive to a very narrow band of environmental stimulation. Specialised to the sensory organ to gain information about a specific domain of environment.
Anatomy of the eye
Vision is made possible by the specialised receptor cells contained within the eyes which transducer light energy from the environment
The cornea sits at the front of the eyes 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 humour. Behind that u will find the iris, the pupil and the lens. The pupil allows light to enter the inside of ur eye called the posterior chamber so it can be detected by the receptors within the eye. The posterior is also filled with a jelly like substance called the vitreous humor. The specialised receptor cells adapted to transducer light energy are found in the black layer of cells at the back of the eyeball called the retina. The retina is where specialised receptor cells called rods and cons where the receptors have evolved to transduce light energy into the perception of colour and light
Sensory transduction in the visual system
Light is made up of photons of electromagnetic energy that oscillate with a particular wavelength. The wavelength of light determines its perceived colour and its amplitude determines its energy level or perceived intensity.
Photoreceptors called rods and cons transduce electromagnetic energy (photons of light) into neural activity. When photons of light strike these receptors it can result in a chemical reaction that’s caused the cell to change its electrical potential. Cones allow the visual system to detect and compare the colour content of a visual image. Cones come in three types each most sensitive to a particular wavelength of light, specifically capable of detecting blue, green or red. Cones are densely packed on the retina particularly in the central part of the retina meaning they provide a higher resolution neural response to a visual image. In contrast rods are more sensitive to light particularly to flickering light and are more prevalent in the periphery of the retina making them useful at night when light levels are low and when looking at something out of the corner of our eyes.
Light is focused by the cornea entered the eye through the pupils and is focused again by the lens to cast a clear and focused image onto the retina at the back of the eye. Cornea is more optically powerful than the lens but the lens has the property of being able to adjust thickness thereby altering refractive power rendered to as accomodation. The rods and cones reside in the deepest layer of the retina light reaching them is transduced into neural activity affecting the activity of retinal ganglion cells retinal ganglion cells are in the uppermost layer of the retina. The axons of ganglion cells carry visual information as neural impulses from each eye to the brain by the optic nerve. The optic nerve are bundles of axons of the retinal ganglion cells.
Visual information from the optic nerve of each eye is relayed through the thalamus to the visual cortex
For axons to leave an area of the eye is left without retinal cells and is thus blind each eye has one. Often our brain fills this in and it is unnoticeable
The neurons of the occipital lobe involved in processing visual information are part of the primary visual cortex the neurons of the visual cortex use the activity received from the eyes to signal our brains the presence of basic visual features such as location, orientation, width and direction of motion of objects in the environment. These neurons receive and interstate inputs from many thalamic cells which allows us to perceive highly complex visual information including colour, depth and motion
Visual sensory disorders
Some visual disorders are due to the anatomy of the eye. Including issues with the optics that prevent light from being focused properly onto the retina. If the cornea or lens is too strong it makes someone near sighted (myopia) only clearly seeing objects near them if the cornea or lens is too weak the person is said to be far sighted (hyperopia) accomodation is important because as an object moved closer a person is able to change the refraction of light coming off the object keeping it in focus. Presbyopia where accomodation is decreased with age making it harder to see objects close to us as we age.
Other ocular problems relate to the functioning of the retinal cells. For example not everyone has three types of properly functioning cones influencing a person ability to see colour. One in fifty mostly males is deficient in their red or green cones making it difficult to distinguish between reds and greens
Perception if colour
Trichromacy theory states the colour we perceive an object depends on the relative activity of our three types of cone. That is the relative activity of red, green and blue light being emitted from an object can uniquely code for 16 million different colours. Like the theory that every colour can be made with the primary colours red yellow and blue.
In contrast opponent process theory states the colour we perceive an object depends on the relative activity of the three pairings of colour sensitive neurons in which the activity of one member of each pair inhibits activity if the other. The pairing are red-green, blue-yellow (yellow as the combination of red and green) and black-white. Opponent processing means for example that the redness of an object can be increased by increasing the amount of red light emitted by that object or by decreasing the amount of green light emitted by that object
Perception of depth
Determining relative distance is tricky because the world is three dimensional while the inner surface of our eyes is flat so condensed information to two dimensions. Various principles guide the way in which visual informations works to enable 3D perceptions some of these using one eye hence monocular depth cues
One clue to relative depth is relative motion. With things further away from us moving perceptively slower than things closer to us.
Another clue is occlusion which means to block or obstruct which refers to whether one object partially or fully blocks the view of another object.
Depth information can also be inferred by comparison of the information received between the eyes which are called binocular cues. Convergence and divergence refer to the extent to which our eyes need to cross for us to focus on an object is a cue to our brain for the distance of that object. Binocular disparity (or retinal disparity or stereopdid) comes from comparison of visual information between eyes when fixating on an object the image will be projected into the same spot on the Regina of each eye: the dead centre
However objects further or closer from the fixation point will not fall on dead centre the locations of those two images on your retinas would start to diverge or converge respectively. There are specialised neurons in the visual cortex that compare the inputs received from each eye and they respond best when their preferred stimulus is at a particular distance from wherever it happens to be you are looking at thus how strongly these neurons in the visual cortex respond to the information from the left vs right eye can help determine the relative depth of objects in the environments
Perception of depth
Determining relative distance is tricky because the world is three dimensional while the inner surface of our eyes is flat so condensed information to two dimensions. Various principles guide the way in which visual informations works to enable 3D perceptions some of these using one eye hence monocular depth cues
One clue to relative depth is relative motion. With things further away from us moving perceptively slower than things closer to us.
Another clue is occlusion which means to block or obstruct which refers to whether one object partially or fully blocks the view of another object.
Depth information can also be inferred by comparison of the information received between the eyes which are called binocular cues. Convergence and divergence refer to the extent to which our eyes need to cross for us to focus on an object is a cue to our brain for the distance of that object. Binocular disparity (or retinal disparity or stereopdid) comes from comparison of visual information between eyes when fixating on an object the image will be projected into the same spot on the Regina of each eye: the dead centre
However objects further or closer from the fixation point will not fall on dead centre the locations of those two images on your retinas would start to diverge or converge respectively. There are specialised neurons in the visual cortex that compare the inputs received from each eye and they respond best when their preferred stimulus is at a particular distance from wherever it happens to be you are looking at thus how strongly these neurons in the visual cortex respond to the information from the left vs right eye can help determine the relative depth of objects in the environments
Perception of motion
Motion is another fundamental perceptual feature of our visual system. There are 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. One illusion that demonstrates this is the beta effect in old cartoon shows artists present a series of still images in quick succession with the location of each image changed ever so slightly frame to frame. Doing this quick enough creates the illusion of fluid motion.
We can also perceive motion using the phi phenomenon, if two seperate images are alternated on and off in quick succession we will perceive the illusion of motion between the two images. Compelling even when the two images are markedly different in their shake size and colour. In both illusions the perception of motion happens automatically without cognitive intervention simply because the pattern of visual stimulation activates the motion detectors in the cortex. The activity if these neurons explains persistence if vision.
Hearing and the auditory system
Specialised receptor cells within the ears sense vibrational energy emitted from objects in the environment and transduce these vibrations to determine sound that the object is making. Sounds are vibrational energy in the form of pressure waves emanating from some vibrating object. The pressure waves can be carried by any compressible medium but most commonly for us humans are carried by air molecules. When these pressures enter the ear canal the vibrations can be transduced by the receptor cells inside the ear to be converted to the rich tapestry of sounds humans are capable of hearing.
Properties of sound waves
Amplitude: the amplitude of the wave corresponded to the intensity of a sound this is measured in decibels and is perceived as the loudness of a sound
Frequency: the frequency of the sound is measured in cycle per second in Hertz and correspond to the perceived tone or pitch or a sound. Sound waves with higher frequency are higher in pitch. Humans can hear sounds frequencies ranging from 20 Hz to 20,000 Hz
Properties of sound waves
Amplitude: the amplitude of the wave corresponded to the intensity of a sound this is measured in decibels and is perceived as the loudness of a sound
Frequency: the frequency of the sound is measured in cycle per second in Hertz and correspond to the perceived tone or pitch or a sound. Sound waves with higher frequency are higher in pitch. Humans can hear sounds frequencies ranging from 20 Hz to 20,000 Hz
Anatomy of the human ear
The fleshy structure on the side of our heads is called the pinnae the outermost section of the ear. This outer layer plays a role in directing vibrational energies from the environment into our middle ear so that vibrations can be transduced into auditory information by the inner ear. Sound waves are focused via the pinnae (or auricle) causing the ear drum (tympanic membrane) to vibrate. Three delicate interconnected bones of the middle ear, the hammer (malleus), anvil (incus) and stirrup (stapes) collectively referred to as the ossicles amplify the vibrations of the ear to compensate for the large loss of mechanical energy. The cochlea receives the vibrational energy in the form of push pull pulsations from the stirrups of the middle ear into 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 over within the cochlea. The vibrational energy is transduced into neural signals which can be processed by the auditory system into sounds. Which occurs through specialised sensory receptors called hair calls called this as they have little hairs (cillia) sprouting from the top. Which is what is sensitive to vibrational energy.
Sound waves entering the cochlea create shearing forces between the basilar membrane (where hair cells sit) and tectorial membrane (where hairs are embedded) the back and forth shearing movements of these membranes (one per Hz of sound wave) results in neural impulses that correspond to frequency of the sound source. As the membranes oscillate the hair cells between the membrane are jerked back and forth resulting in electrical pulses
Anatomy of the human ear
Pinnae is the outer structure of the ear and directs and focuses sound waves and vibrational energies into our middle ear so that the vibrations can be transduced into auditory information by the inner ear.
The sound waves focused via the pinnae are directed into the ear canal, causing the ear drum (tympanic membrane) to vibrate. Three interconnected bones of the middle ear, the hammer (malleus), anvil (incus) and stirrup (stales) collectively referred to as the ossicles amplify the vibrations of the ear drum to compensate for any mechanical energy loss. Push pull pulsations from the stirrups are received by the cochlea onto the oval window which are attached to the stirrups. The vibrational energy passes down along the cochlea in oscillations of the basilar membrane and tectorial membrane with one sitting above the other in the cochlea
The vibrational energy is transduced by specialised sensory receptors called hair cells, called this as they have little hairs (cillia) sprouting from the top. These hairs are what is sensitive to the vibrational energy and serve to transduce the energy into a neural signal. This occurs by sound waves entering the cochlea create shearing forces between the basilar and tectorial membranes. This shearing movements (one per Hz of sound wave) results in neural impulses that correspond to the vibrational frequency of the sound source. When the basilar and tectorial membrane oscillate the hair cells are jerked back and forth each push can result in an electrochemical impulse being sent from the hair cell. These electrochemical signals result in impulses being sent along axons collectively referred to as the auditory nerve to the brain.
Information from each auditory nerve is sent to the brain stem then relayed via the thalamus to the auditory cortex for processing. Neurons of auditory cortex integrate inputs from numerous thalamic cells, typically selectively responding to pure tones of sound, the sound of a particular frequency (pitch). The neurons of auditory cortex are arranged tonotopically, meaning neurons are sensitive to progressively higher frequency as we move further along the cortex towards the back of the brain.
