Midterm #2 Flashcards
Computer vision: Object recognition
Detection of objects in an image and then matching those objects to existing, stored representations of what those objects are to create a secene.
Why is it hard to design a perceiving machine?
The stimulus on the receptors is ambiguous (inverse projection problem). Objects can be hidden or blurred (occlusions are common in the environment. Objects look different from different viewpoints (Viewpoint invariance).
Inverse projection problem
The fact that a particular image on the retina (or a computer vision machine’s sensors) can be caused by an infinite number of objects.
Viewpoint invariance
The ability to recognize an object regardless of the viewpoint. This is a difficult task for computers to perform.
Perceptual Organization
Approach established by Wundt in the late 1800s. States that perceptions are created by combining elements called sensations. Stimulated the founding of Gestalt psychology. The whole differs from the sum of its parts: perception is not built up form sensations but is a result of perceptual organization.
Structuralism
Wilhelm Wundt. Perceptions are created by combining elements called sensations. Distinguished between sensations and perceptions.
Apparent movement
An illusion of movement. When two stimuli that are in slightly different positions are flashed one after another with the correct timing, movement is perceived between the two stimuli. But there is actually movement in the display, just two stationary stimuli flashing on and off.
Illusory contours
Appear real but have physical edge. Illusory contours represent the edges of the cube. Called illusory because they aren’t actually present in the physical stimulus.
The Gestalt Laws of Perceptual organization
Involves the grouping of elements in an image to create larger objects.
Gestalt law of Pragnanz
Every stimulus is seen as simply as possible.
Gestalt law of Similarity
Similar things appear to be grouped together.
Gestalt law of Good Continuation
Connected points resulting in straight or smooth curves are seen as belonging together, and the lines tend to be seen in such a way as to follow the smoothest path.
Gestalt law of Proximity
Things that are near each other appear to be grouped together.
Gestalt law of Common Region
Elements that are within the same region of space appear to be grouped together.
Gestalt law of Uniform connectedness
A connected region of visual properties, such as lightness, colour, texture, or motion, is perceived as a single unit.
Gestalt law of Common Fate
Things that are moving in the same direction appear to be grouped together.
Perceptual Segregation
The perceptual seperation of one object from another. Figure-ground segregation: determining what part of the environment is the figure, so that it “stands out” from the background.
The properties of figure and ground
- The figure is more “thinglike” and more memorable than the ground.
- The figure is seen in front of the ground.
- The ground is more uniform and extends behind figure.
- The contour separating figure from the ground belongs to the figure (border ownership).
Figural cues proposed by the Gestalt psychologists
Areas lower in the field of view are more likely to be perceived as figure.
Heuristics
Rules of thumb that provide a best-guess solution to a problem. Gestalt principles are more accurately described as heuristics instead of laws.
An algorithm
A procedure that is guaranteed to solve a problem.
The role of perceptual principles and experience in determining which area is figure.
Gestalt psychologists’ emphasis on perceptual principles led them to minimize the role of a person’s past experiences in determining perception.
Meaningfulness experiment, Gibson and Peterson (1994)
Experiment that argued against the idea of minimizing the role of a person’s past experiences in determining perception by showing that figure-ground formation can be affected by the meaningfulness of a stimulus.
Recognition by Components (RBC) theory
Objects are comprised of individual geometric components called geons. Geons: three-dimensional shapes, like pyra-mids, cubes, and cylinders.
Shortcomings of RBC theory
Many aspects of object perception that the RBC theory could not explain:
Grouping or organization like the Gestalt principles do. Some objects can’t be represented by assemblies og geons. The RBC theory doesn’t allow for distinguishing between objects within a given category.
Non-accidental properties (NAPs).
Properties of edges in the retinal image that correspond to the properties of edges in the three-dimensional environment.
Perceiving Scenes and Objects in Scenes
Scene: 1) background elements, 2) multiple objects that are organized in a meaningful way relative to each other and the background.
Objects: compact and acted upon.
Scenes: Extended in space and are acted within.
Discriminability of geons
The fact that each geon has a unique set of NAPs results in a property of geons called discriminability - each geon can be discriminated from other geons.
Geons and Viewpoint invariance
The fact that NAPs are visible from most viewpoints results in property of geons called viewpoint invariance - the geon can be identified when viewed from most viewpoints.
Principle of componential recovery
The ability to identify an object if we can identify its geons. This principle is what is behind our ability to identify objects in the natural environment even when parts of the objects are hidden by other objects.
Gist of a scene
Perceiving scenes presents a paradox: scenes are often large and complex, however, despite this size and complexity, you can identify most scenes after viewing them for only a fraction of a second.
What enables observers to perceive the gist of a scene so rapidly?
Global image features: can be perceived rapidly and are associated with specific types of scenes. Past experiences in perceiving properties of the environment: blue associated with open sky, landscapes are often green and smooth, verticals and horizontals are associated with buildings.
Degree of naturalness
Natural scenes have textured zones and undulating contours. Man-made scenes are dominated by straight lines and horizontals and verticals.
Degree of openness
Open scenes, such as the beach, often have a visible horizon line and contain few objects. The forest is an example of a scene with a low degree of openness.
Degree of roughness
Smooth scenes (low roughness) like the beach contain fewer small elements. Scenes with high roughness like the forest contain many small elements and are more complex.
Degree of expansion
The convergence of parallel lines (railroad tracks that appear to vanish in the distance).
Color in scenes
Some scenes have characteristics colours, like the beach scene (blue) and the forest (green and brown).
Physical Regularities
Regularly occurring physical properties of the environment. There are more vertical and horizontal orientations in the environment than oblique (angled) orientations. This occurs in human-made and natural environments.
Light-from-above heuristic
The assumption that light is coming from above. People make this assumption because most light in our environment comes from above.
Semantic Regularities
The characteristics associated with the functions carried out in different types of scenes. What we expect to see in different contexts influences our interpretation of the identity blurry “blobs” in scenes.
The Role of Inference in Perception
People use their knowledge of physical and semantic regularities to infer what is present in a scene.
Helmholtz’s Theory of Unconscious Inference
States that some of our perceptions are the result of unconscious assumptions we make about the environment. Was proposed to account for our ability to create perceptions from stimulus information that can be seen in more than one way.
Likelihood principle
Aspect of the theory of unconscious inference, which states that we perceive the object that is most likely to have caused the pattern of stimuli that we have received.
Bayesian inference
We perceive what is most likely to have created the stimulation we have received in terms of probabilities.
Contextual Modulation
When we add a field of randomly oriented lines, these lines, which fall outside the neuron’s receptive field, cause a decrease in how rapidly the neuron fires to the single vertical line. This effect of the stimuli that fall outside of the neuron’s receptive field is called contextual modulation, because the context within which the bar appears affects the neuron’s response to the bar.
How does the brain respond to objects?
Objects are represented by distributed coding, so a specific face would be represented by the pattern of firing of a number of neurons that respond to faces. There is a distributed system in the cortex for perceiving faces. The activation caused by other objects is also distributed, with most objects activating a number of different areas in the brain.
Binocular rivalry
Connections between neural responses and perception have been determined by using this perceptual phenomenon: if one image is presented to the left eye and a different image is presented to the right eye, perception alternates back and forth between the two eyes.
Predictive coding
A theory that describes how the brain uses our past experiences - our our “priors,” as Bayes put it - to predict what we will perceive. A way that the brain implements prediction.
Lateral occipital complex (LOC)
Active when the person views any kind of object (animal, face, house, or tool) but not when they view a texture, or an object with the parts scrambled. Builds upon the processing that took place in lower-level visual regions.
The Neural Correlates of Face Perception (FFA)
Fusiform face area (FFA): fMRI to determine brain activity in response to pictures of faces and other objects such as household objects, houses, and hands. Subtracted the response to the other objects form the response to the faces.
Prosopagnosia
Difficulty recognizing the faces of familiar people.
Neural representation of other categories of objects
Exrastriate body area (EBA): activated by pictures of bodies and parts of bodies.
Neural representation of other categories of objects, Alex Huth and coworkers (2012).
Participants viewed 2 hours of film clips while in a brain scanner. Analyze how individual brain areas were activated by different objects and actions in the films.
Brain responses to Scenes
Parahippocampal place area (PPA) (parahippocampal cortex (PHC)). Spatial layout hypothesis.
The relationship between perception and brain activity, Frank Tong and coworkers (1998).
Binocular rivalry. When the observers perceived the house, activity occured in the parahippocampal place area (PPA) in the left and right hemispheres (red ellipses). When observers perceived the face, activity occurred in the fusiform face area (FFA) in the left hemisphere (green ellipse).
Akinetopsia
Motion blindness. Motion is either very difficult or impossible to perceive. Traumatic brain injury. Neurodegenerative disease such as Alzheimer’s. Epilepsy, hallucinogen persistent perception disorder (HPPD). Damage to V5 medial temporal.
L.M.
Lost the ability to perceive motion when she suffered a stroke that damaged an area of her cortex involved in motion perception. Her condition is called motion agnosia, and made it difficult for her to pour tea or coffee into a cup because the liquid appeared frozen. Another effect was the sudden appearance or disappearance of people and objects.
Attentional capture
The ability of motion to attract attention. This effect occurs not only when you are consciously looking for something, but also while you are paying attention to something else.
Real motion
Actual motion of an object. Perceiving a car driving by, people walking. Observers perceive shapes more rapidly and accurately when an object is moving.
Illusory motion
Perception of motion when there actually is none. Eg., apparent motion: no actual motion between the stimuli.
Induced motion
Occurs when motion of one objects (usually a large one) causes a nearby stationary object (usually a smaller one) to appear to move.
Motion aftereffects
Occur after viewing a moving stimulus for 30 to 60 seconds and viewing a stationary stimulus, which appears to move. Eg,, waterfall illusion.
Movement as an organizing function
Movement serves an organizing function which groups smaller elements into larger units. The motion of individual birds becomes perceived as the larger unit of the flock, in which the birds are flying in synchrony with each other.
Biological movement
When a person or animal moves, movement of individual units - arms, legs, and body - become coordinated with each other.
Event
Segment of time at a particular location that is perceived by observers to have a beginning and an end.
Event boundary
The point in time when each of these events ends and the next one begins. Perception of movement plays an important role in separating activities into meaningful events. More likely to occur when there is change in speed or acceleration of movement.
Social perception
Social cues are often linked to movement. Point-light walkers:
1) Social interaction: the people were near interacting in various ways.
2) Non-social interaction: the people were near each other but were acting independently. The observers were able to indicate whether the two people were interacting with each other or were acting independently.
Taking action
Navigating through the environment (safely). Watching and playing sports. Pouring drinks etc.
The Ecological Approach to Motion Perception
Looking for information in the environment that is useful for perception. According to Gibson, information is located not on the retina but “out there” in the environment. Optic Array.
Optic Array
The structure created by the surfaces, textures, and contours of the environment. Gibson focused on how movement of the observer causes changes in the optic array.
Local disturbance in the optic array
Objects are covered then uncovered. Because person moves relative to stationary cues, movement is perceived.
Global optic flow
This signals that the environment is stationary and that the observer is moving. Everything moves to the left at once signalling no movement.
Aperture problem
The fact that viewing only a small portion of a larger stimulus can result in misleading information about the direction in which the stimulus is moving.
Coherence
Willaim Newsome and coworkers used a computer to create moving-dot displays in which the direction of motion of individual dots can be varied. Newsome coined the term coherence to indicate the degree to which the dots move in the same direction.
Corollary Discharge Theory
Considering the neural signals that travel from the eye to the brain.
Three signals:
1) The image displacement signal, which occurs when an image moves across the retina.
2) The motor signal, which is sent from the motor area to the eye muscles to cause the eye to move.
3) The corollary discharge signal, which is a copy of the motor signal.
Movement will be perceived if a brain structure called the comparator (actually a number of brain structures) receives just one signal.
The Reichardt Detector
The Reichardt detector circuit: A and B, which send their signals to an output unit that compares the signals it receives from neurons A and B. Delay unit: Slows down the signals from A as they travel toward the output unit. The output unit multiplies the responses from A and B to create the movement signal that results in the perception of motion.
Real-motion neuron
Responds only when the stimulus moves and doesn’t respond when the eye moves, even though the stimulus on the retina is the same in both situations.
Point-light walker stimulus
Information about people’s actions, intentions, and moods can also be obtained based solely on motion information. Point-light walker stimuli were created to demonstrate this by placing small lights on people’s joints and then filming the patterns created by these lights when people worked and carried out other actions in the dark.
Single-Neuron Responses to Motion
Middle temporal area. Experiments Using Moving Dot Displays. A coherence increase: 1) the monkey judged the direction of motion more accurately. 2) the MT neuron fired more vigorously.
Implied motion
A situation in which a still picture depicts a situation involving motion.
Representational momentum
The idea that the motion depicted in a picture tends to continue in the observers’ mind.
Chromatic colors or hues
When some wavelengths are reflected more than others.
Selective reflection
Property of reflecting some wavelengths more than others, which is a characteristic of chromatic colours.
Achromatic colours
When the light reflection is similar across the full spectrum (contains no hue), as in white, black, and all the grays in between.
Selective transmission
In the case of things that are transparent (liquids, plastics, glass) chromatic colour is created by selective transmission, meaning that only some wavelengths pass through the object or substance.
What happens when coloured lights are superimposed (mixed)?
All of the light that is reflected from the surface by each light when alone is also reflected when the lights are superimposed. Mixing lights is called additive colour mixture.
What happens when coloured paints are mixed together?
When mixed, both paints still absorb the same wavelengths they absorbed when alone, so the only wavelengths reflected are those that are reflected by both paints in common. Mixing paints is called subtractive colour mixture.
Summarization of the connection between wavelength and colour
Colours of light are associated with wavelengths in the visible spectrum. The colours of objects are associated with which wavelengths are reflected (opaque objects) or transmitted (transparent objects). The colours that occur when we mix colours are also associated with which wavelengths are reflected into the eye. Mixing lights causes more wavelengths to be reflected, mixing paints causes fewer wavelengths to be reflected.
Trichromatic theory of colour vision
States that colour vision depends on the activity of three different receptor mechanisms. Based on the results of a psychophysical procedure called colour matching.
Helmholtz’s colour-matching experiments
Observers adjusted the amounts of three different wavelengths of light mixed together in a “comparison field” until the colour of this mixture matched the colour of a single wavelength in a “test field”. The key findings: Any reference colour could be matched provided that observers were able to adjust the proportions of three wave-lengths in the comparison field. Two wavelengths allowed participants to match some, but not all, reference colours. They never needed four wavelengths to match any reference colour.
Cerebral achromatopsia
A type of colour-blindness caused by damage to the cerebral cortex of the brain, rather than abnormalities in the cells of the eye’s retina. Damage to the ventro-medial occipital and temporal lobes.
Colour deficiency or Congenital achromatopsia
Occurs at birth because of the genetic absence of one or more types of cone receptors. Most people who are born partially colour blind are not disturbed by their decreased colour perception compared to “normal”. They have never experienced colour as a person with normal colour vision does. People can perceive colour but have difficulty distinguishing between certain colours, such as red and green.
Functions of colour perceptions
Signalling functions: Help us identify and classify things. Perceptual organization. The ability to detect coloured food has led to the proposal that monkey and human colour vision may have evolved for the express purpose of detecting fruit. Colour can be a cue to emotions signalled by facial expressions.
Colour and Light: Newton’s experiment
- He made a hole in a window shade, which let a beam of sunlight enter the room. When he placed Prism 1 in its path, the beam of white-appearing light was split into the components of the visual spectrum.
- He thought that white light was a mixture of differently coloured lights and that the prism separated the white light into its individual components.
- Newton next placed a board in the path of the differently coloured beams. Holes in the board allowed only particular beams to pass through while the rest were blocked. Each beam that passed through the board then went through a second prism.
2 important things that Newton noticed about the light that passed through the second prism in his experiment
- The second prism did not change the colour appearance of any light that passed through.
- The degree to which beams from each part of the spectrum were “bent” by the second prism was different.
Newton’s conclusion in his colour and light experiment
He concluded that light in each part of the spectrum is defined by different physical properties and that these physical differences give rise to our perception of different colours.
Mixing Lights - Additive colour mixing
If a light that appears blue is projected onto a white surface and a light that appears yellow is projected on top of the light that appears blue, the area where the lights are superimposed is perceived as white. Therefore, added together light contains short, medium, and long wavelengths.
Spectral colours
Colours evoked by monochromatic light (i.e., a pure wavelength of light).
Non-spectral colours
Colours that do not appear in the spectrum because they are mixtures of other colours, such as magenta (a mixture of blue and red).
How many colours?
Estimation that humans can tell the difference between about 2.3 million different colours.
Examples of hues
Red, orange, yellow, green, blue, violet.
Saturation
Refers to the intensity of colour.
Value
The light-to-dark dimension of colour.
Colour solid
Illustrates the relationship among huge, saturation, and value.
Newton’s proposal of the Trichromatic Theory of Colour Vision
Each component of the spectrum must stimulate the retina differently in order for us to perceive colour.
Evidence for the Trichromatic Theory
Researchers measured absorption spectra of visual pigments in receptors. They found pigments that responded maximally to: short wavelengths, medium wavelengths, long wavelengths. Later researchers found genetic differences for coding proteins for the three pigments.
Cone Responding and Colour Perception
Colour perception is based on the response of the three different types of cones.
Microspectrophotometry
A technique used to measure the absorption or transmission of a solid or liquid material in either transmitted or reflected light. Responses vary depending on the wavelengths available. Combinations of the responses across all three cone types lead to perception of all colours.
Adaptive optical imaging
Taking pictures that show how the cones are arranged on the surface of the retina. Cone Mosaic.
Metamerism
A situation in which two physically different stimuli are perceptually identical. The two identical fields in a colour-matching experiment are called metamers.
Monochromatism
A rare form of colour blindness. Monochromats have no functioning cones, so their vision is created only by the rods. They can match any wavelength in the spectrum by adjusting the intensity of any other wavelength. So, they only need one wavelength to match any colour in the spectrum and see only in shades of grey.
Principle of univariance
Absorption of a photon causes the same effect, no matter what the wavelength is. Any two wavelengths can cause the same response by changing the intensity. Two receptor types (dichromats) solve this problem but three types (trichromats) allow for the perception of more colours.
Dichromat
Needs only two wavelength to match all other wavelengths on the spectrum. See chromatic colours, but cannot distinguish among all colours.
Protanopia
A form of dichromatism. A protanope is missing the long-wavelength pigment. They perceive short-wavelength light as blue, and as the wavelength is increased, the blue becomes less and less saturated, until, at 492 nm, the protanope perceives gray. The wavelength at which they perceive gray is called the neutral point. At wavelengths above the neutral point, the protanope perceives yellow, which becomes less intense at the long wavelength end of the spectrum.
Deuteranopia
A form of Dichromatism. A deuteranope is missing the medium-wavelength pigment. They perceive blue at short wavelengths, sees yellow at long wavelengths, and has a neutral point at about 498nm.
Tritanopia
A form of dichromatism. Very rare. A tritanope is missing the short-wavelength pigment. They see blue at short wavelengths, red at long wavelengths, and a neutral point at 570 nm.
Anomalous trichromatism
An anomalous trichromat needs three wavelengths to match any wavelength, just as a normal trichromat does. However, they mix these wavelengths in different proportions from a trichromat, and they are not as good as a trichromat at discriminating between wavelengths that are close together.
Unilateral dichromat
A person with trichromatic vision in one eye and dichromatic vision in the other. To determine what a dichromat perceives, you need to use a unilateral dichromat. Both of their eyes are connected to the same brain, so this person can look at a colour with their dichromatic eye and then determine which colour it corresponds to in his trichromatic eye.
The Opponent-Process Theory of Colour Vision
Colour vision is caused by opposing responses generated by blue and yellow, and by green and red.
Behavioural evidence of The Opponent-Process Theory of Colour Vision
Colour afterimages and simultaneous colour contrast show the opposing pairings. Types of colour blindness are red/green and blue/yellow.
Opponent-process mechanism proposed by Hering
Three mechanisms: red/green, blue/yellow, and white/black. The pairs respond in an opposing fashion, such as positively to red and negatively to green. These responses were believed to be the result of chemical reactions in the retina. Proposed that each of the other colours are made up of a combination of the primary colours (red, yellow, green, blue). Hue scaling: participants were given colours from around the hue circle and told to indicate the proportions of the primary colours that they perceived in each colour.
Why was Hering’s opponent-mechanism proposal not widely accepted?
- Its main competition, trichromatic theory, was championed by Helmholtz, who had great prestige.
2) Hering’s phenomenological evidence, which was based on describing the appearance of colours, could not compete with Maxwell’s quantitative colour mixing data.
3) There was no neural mechanism known at that time that could respond in opposite ways.
Evidence for the Opponent-Process Theory
Psychophysical Evidence: Hue cancellation experiments. Hurvich and Jameson’s (1957). They provided quantitative measurements of the strengths of B-Y and R-G components of the opponent mechanisms. Researchers performing single-cell recordings found opponent neurons.
Opponent neurons
They are located in the retina and LGN. Respond in an excitatory manner to one end of the spectrum. and an inhibitory manner to the other.
How Opponent Responding can be created by three types of receptors
Each theory describes the physiological mechanisms in the visual system. Trichromatic theory explains the responses of the cones in the retina. Opponent-process theory explains neural response for cells connected to the cones further in the brain.
Memory colour
Another thing that helps achieve colour constancy is our knowledge about the usual colours of objects in the environment. It is an effect on perception of prior knowledge of the typical colours of objects.
Ratio principle
According to the ratio principle, as long as the ratio of reflectance of the object to the reflectance of surrounding objects remains the same, the perceived lightness will remain the same.
Reflectance edge
An edge where the reflectance of two surfaces changes.
Illumination edge
An edge where the lightness changes.
Physical definition of sound
Sound is pressure changes in the air or other medium
Perceptual definition of sound
Sound is the experience we have when we hear
How do loud speakers produce sound through a process?
The diaphragm of the speaker moves out, pushing air molecules together called condensation. The diaphragm also moves in, pulling the air molecules apart called rarefaction. The cycle of this process creates alternating high and low pressure regions that travel through the air.
Amplitude
Difference in pressure between high and low peaks of wave. Perception of amplitude is known as loudness. Decibel (dB) is used as the measure of loudness.
Pure Tones
Occurs when pressure changes in the air occur in a pattern described by a mathematical function called a sine wave.
Frequency
Number of cycles within a given time period. Measured in Hertz (Hz): 1 Hz is one cycle per second. Perception of pitch is related to frequency. Tone height is the increase in pitch that happens when frequency is increased.
Complex Tones and Frequency Spectra
Both pure and some complex tones are periodic tones.
Fundamental frequency
The repetition rate of a complex tone is called the fundamental frequency of the tone.
Periodic complex tones
Consist of several pure tones called harmonics.
Additional harmonics
Multiple of the fundamental frequency
Additive synthesis
We can “build” a complex tone by using a technique called additive synthesis, in which a number of sine-wave components are added together to create the complex tone.
Frequency spectrum
Display of harmonics of a complex sound. The position of each line on the horizontal axis indicates the harmonic’s frequency, and the height of the line indicates the harmonic’s amplitude.
Loudness
Loudness is the perceptual quality most closely related to the level or amplitude of an auditory stimulus.
Audibility curve
Shows the threshold of hearing in relation to frequency. Changes on this curve show that humans are most sensitive to 2,000 to 4,000 Hz.
Auditory response area
Falls between the audibility curve and the threshold for feeling. It shows the range of response for human audition.
Equal loudness curve
Determined by using a standard 1,000 Hz tone. Two dB levels are used: 40 and 80. Participants match the perceived loudness of all other tones to the 1,000 Hz standard. Resulting curves show that tones sound: at almost equal loudness at 80 dB, softer at 40 dB for high and low frequencies than the rest of the tones in the range.
Pitch
The perceptual quality we describe as high and low
Timbre
All other perceptual aspects of a sound besides loudness, pitch, and duration. It is closely related to the harmonics, attack, and decay of a tone.
Effect of missing fundamental frequency
Removal of the first harmonic results in a sound with the same perceived pitch, but with a different timbre. This is called periodicity pitch.
Attack of tones
Buildup of sound at the beginning of a tone
Decay of tones
Decrease in sound at the end of tone
Outer ear
Pinna and auditory canal. Pinna helps with sound location. Auditory canal protects the tympanic membrane at the end of the canal. The resonant frequency of the canal amplifies frequencies between 1,000 and 5,000 Hz.
Middle ear
Two cubic centimeter cavity separating inner from outer ear. Contains three ossicles:
1. Malleus: moves to the vibration of the tympanic membrane.
2. Incus: transmits vibrations of malleus.
3. Stapes: transmits vibrations of incus to the inner ear via the oval window of the cochlea.
Functioning of ossicles
Outer and inner ear are filled with air. Inner ear is filled with fluid that is much denser than air. Pressure changes in air transmit poorly into the denser medium. Ossicles act to amplify the vibration for better transmission to the fluid. Middle ear muscles dampen the ossicles’ vibrations to protect the inner ear from potentially damaging stimuli.
The Inner Ear
The main structure of the inner ear is the liquid-filled cochlea, which is a snail-like structure. The liquid inside the cochlea is set into vibration by the movement of the stapes against the oval window.
Basilar membrane
Vibrates in response to sound and supports the organ of Corti.
Inner and outer hair cells
Are the receptors for hearing.
Tectorial membrane
Extends over the hair cells
Process of transduction in ear
Cilia bend in response to movement of the organ of Corti and the tectorial membrane. Movement in one direction opens ion channels. Movement in the other direction closes the channels. This causes bursts of electrical signals.
Bekesy’s Place Theory of Hearing
Frequency of sound is indicated by the place on the organ of Corti that has the highest firing rate.
Tonotopic Mao
Cochlea shows an orderly map of frequencies along its length. Apex responds best to low frequencies, base responds best to high frequencies.
Neural frequency tuning curves
Pure tones are used to determine the threshold for specific frequencies measured at single neurons. Plotting thresholds for frequencies results in tuning curves. Frequency to which the neuron is most sensitive is the characteristic frequency.
Place Theory
Based on the relation between a sound’s frequency and the place along the basilar membrane that is activated.
Phase locking
Property of firing at the same place in the sound stimulus. Nerve fibers fire in bursts. Firing bursts happen at or near the peak of the sine-wave stimulus. Thus, they are “locked in phase” with the wave. Groups of fibers fire with periods of silent intervals creating a pattern of firing.
Auditory masking
Occurs in everyday experience any time your ability to hear a sound is decreased by the presence of other sounds.
Temporal coding
The connection between the frequency of a sound stimulus and the timing of the auditory nerve fiber.
3 reasons that hearing loss can occur
1) Blockage of sound from reaching the receptors, called conductive hearing loss.
2) Damage to the hair cells
3) Damage to the auditory nerve or the brain.
Sesnorineural hearing loss
Hearing loss due to damage to the hair cells, auditory nerve, or brain.
Presbycusis
Most common form of sensorineural hearing loss. Greatest loss at high frequencies. Affects males more severely than females. Appears to be caused by exposure to damaging noises or drugs.
Noise-induced hearing loss
Occurs when loud noises cause degeneration of the hair cells. Leisure noise can also cause hearing loss.
Cochlear Implants
Electrodes are inserted into the cochlea to electrically stimulate auditory nerve fibers. The device is made up of: A microphone worn behind the ear, a sound processor, a transmitter mounted on the mastoid bone, a receiver surgically mounted on the mastoid bone.
Pathway from the cochlea to the cortex (brain)
Auditory nerve fibers from the cochlea synapse in a sequence of subcortical structures (structures below the cerebral cortex). Begins with cochlear nucleus, and then SONIC MG: superior olivary nuclei in the brain stem, the inferior colliculus in the mid-brain, and the medial geniculate nucleus, in the thalamus. From there, fibers continue to the primary auditory receiving area (A1) in the temporal lobe of the cortex.
Auditory Areas in the Cortex
Cortical processing starts with a core area: includes the primary auditory cortex (A1) and some nearby areas. Signals then travel to an area surrounding the core, called the belt area, and then to the parabelt area.
Hierarchical processing
Signals are first processed in the core and then travel to the belt and then to the parabelt.
Pitch neurons
Cortical neurons that respond only to stimuli associated with the 182-Hz tone, which is associated with a specific pitch.
