Week 9 & 10 - Sensation and Perception Flashcards
Sense
Is a system that translates information from outside the nervous system into neural activity
Sensations
Are messages from the senses that make up the raw information that affects many kinds of behaviour and mental processes
How do we sense?
With accessory structures and transduction
All of these senses respond to:
Incoming stimulus energy, encode it in the form of nerve cell activity, and send this coded information to the brain
Accessory structures
Are structures, such as the lens of the eye, that modify a stimulus. It reshapes the light or sound or other energy that comes to us from the environment.
Transduction
Is the process of converting incoming energy into neural activity.
Elements of the Sensory System:
Energy contains information about the world. 1. Accessory structure modifies energy. 2. Receptor transduces energy into neural activity. 3. Sensory nerves transfer the neural activity to the central nervous system. 4. Thalamus processes and relays the neural activity to the cerebral cortex. 5. Cerebral cortex receives input and produces the sensation and perception.
Neural receptors
Are specialised cells that detect certain forms of energy and transduce them into nerve cell activity
Sensory adaptation
Is the process through which responsiveness to an unchanging stimulus decreases over time
Encoding
Is the process of acquiring information and entering it into memory
Specific Energy Doctrine
Is the discovery that stimulation of a particular sensory nerve provides codes for that sense, no matter how the stimulation takes pla
How can psychologists measure perceptions when there is no way to get inside people’s heads to experience what they are experiencing?
One solution to this problem is to present people with lights, sounds and other stimuli and ask them to report their perception of the stimuli. This method of studying perception, called psychophysics, describes the relationship between physical energy in the environment and our psychological experience of that energy.
How strong must a stimulus be in order to trigger a conscious perceptual experience?
Not very strong. Normal human vision can detect the light equivalent to a candle flame burning in the dark nearly 50 kilometres away.
Absolute threshold
The smallest amount of light, sound, pressure or other physical energy that can be detected 50 per cent of the time. Example: the tick of a watch from 6 metres away.
Subliminal stimulation
Stimulation that is below the threshold that is too weak or too brief for us to notice.
Supraliminal stimulation.
Stimulation that is above the absolute threshold and thus consistently perceived by humans. The stimulation that is strong.
Signal detection theory
Presents a mathematical model of how your personal sensitivity and response bias combine to determine your decision about whether or not a near-threshold stimulus occurred.
Just-noticeable difference (JND)
Is the smallest detectable difference in stimulus energy
Weber’s law
Is a law stating that the smallest detectable difference in stimulus energy is a constant fraction of the intensity of the stimulus. This fraction, often called Weber’s constant or Weber’s fraction, is given the symbol K. K is different for each of the senses. The smaller K is, the more sensitive a sense is to stimulus differences.
Magnitude estimation
Refers to how our perception of stimulus intensity is related to the actual strength of the stimulus (Fechner’s law).
Types of human senses:
Vision Hearing Smell Touch Taste
Sound
Is a repeated fluctuation, a rising and falling, in the pressure of air, water or some other substance called a medium.
When you speak your vocal cords vibrate, producing fluctuations in air pressure that spread as waves. A wave is:
A repeated, rhythmic variation in pressure that spreads out in all directions.
Physical characteristics of sound
Sound can be represented graphically by waveforms.
Three characteristics of sound waveforms:
Amplitude (the difference between the peak and the baseline of a waveform). Wavelength (the distance from one peak to the next in a waveform). Frequency (the number of complete waveforms, or cycles, that pass a given point in space every second). Frequency is described in a unit called hertz (Hz). One cycle per second is 1 Hz.
Are the wavelength and frequency related?
Yes. Because the speed of sound is constant in a given medium, wavelength and frequency are related: the longer the wavelength, the lower the frequency; the shorter the wavelength, the higher the frequency. Most sounds are mixtures of many different frequencies and amplitudes.
The physical characteristics of sound waves (amplitude and frequency) determine the
Psychological dimensions of sound which are: Loudness. Pitch and; Timbre.
Loudness
is determined by the amplitude of the sound wave; waves with greater amplitude create sensations of louder sounds. Loudness is described in units called decibels, abbreviated to dB. By definition, 0 dB is the minimum detectable sound for normal hearing.
Pitch
How high or low a tone sounds. Humans can hear sounds ranging from about 20 Hz to about 20 000 Hz.
Almost everyone hears relative pitch; that is, people can tell whether one note is higher than, lower than or equal to another note. However, some people have absolute pitch, more commonly known as perfect pitch, which means that:
They can identify specific frequencies and the notes they represent. They can say, for example, that a 262-Hz tone is middle C. Though perfect pitch appears to be an inborn trait, it may also be possible to develop it through learning.
Timbre
Is the mixture of frequencies and amplitudes that make up the quality of sound. It is determined by complex wave patterns that are added onto the lowest, or fundamental, frequency of a sound.The extra waves allow you to tell, for example, the difference between a note played on a flute and the same note played on a clarinet.
The human ear converts sound energy into:
Nerve cell activity through a series of accessory structures and transduction mechanisms.
The amplitude, frequency and complexity of sound waves determine the:
Loudness, pitch and timbre of sound.
Accessory structures
Pinna, tympanic membrane, malleus, incus, stapes, oval window, basilar membrane
Sound waves are collected in:
The outer ear, beginning with the pinna. The pinna funnels sound down through the ear canal. At the end of the ear canal, the sound waves reach the middle ear, where they strike a tightly stretched membrane known as the eardrum, or tympanic membrane. The sound waves cause matching vibrations in the tympanic membrane. The vibrations of the tympanic membrane then pass through a chain of three tiny bones: the malleus, or hammer; the incus, or anvil; and the stapes, or stirrup. These bones amplify the vibrations coming from the tympanic membrane by focusing them onto a smaller membrane called the oval window. When sound vibrations pass through the oval window, they enter the inner ear, reaching the cochlea.
Cochlea
A fluid-filled spiral structure of the ear in which transduction occurs.
Basilar membrane
The floor of the fluid-filled duct that runs through the cochlea. Whenever a sound wave passes through the fluid in the tube, it causes the basilar membrane to move up and down, and this movement bends hair cells of the organ of Corti, a group of cells resting on the membrane. These hair cells connect with fibres from the acoustic nerve, also known as the auditory nerve. When the hair cells bend, they stimulate neurons in the acoustic nerve to fire, and the pattern of firing creates a coded message that tells the brain about the amplitude and frequency of the incoming sound waves. We experience this information as loudness and pitch.
The acoustic nerve, also known as the auditory nerve is:
A bundle of axons that goes into the brain.
The middle and inner ear are among the most delicate structures in the body. If they deteriorate or are damaged __________________.
Deafness can result.
Types of deafness
Conduction deafness: occurs when the bones of the middle ear fuse together, thus preventing accurate conduction of vibrations from one bone to the next. Nerve deafness, results when the acoustic nerve or, more commonly, the hair cells are damaged. This occurs gradually with age, but it can also be caused more quickly by extended exposure to the noise of jet engines, industrial equipment, gunfire, loud music and other intense sounds.
Before sounds can be heard, the information encoded in the firing of the many axons that make up the acoustic nerve must be sent to the brain for further analysis.This transmission process begins when the acoustic nerve conveys the information to the:
Thalamus. From there, the information is relayed to the primary auditory cortex, an area in the temporal lobe of the brain.
Auditory cortex
Is the area in the brain’s temporal lobe that is the first to receive information about sounds from the thalamus. It is in the primary auditory cortex that information about sound is subjected to the most intense and complex analysis. This auditory analysis may be especially efficient in people who were deprived of visual experience because of blindness in early life.
Preferred frequencies
Is when different cells fire more vigorously in response to sounds of particular frequencies.
The frequency of a _________ determines the ______ that you experience
Sound; Pitch
Frequency is coded in two ways, which are described by the:
Place theory and frequency-matching theory.
Place theory
Is a theory that hair cells at a particular place on the basilar membrane respond most to a particular frequency of sound called a characteristic frequency. In other words, place theory describes a spatial, or place-related, code for frequency. When hair cells at a particular location respond to a sound, we hear a pitch that is at the characteristic frequency of those cells. One important result of this arrangement is that extended exposure to a very loud sound of a particular frequency can destroy hair cells at one spot on the basilar membrane, making it impossible to hear sounds of that frequency.
Frequency-matching theory.
Explains the coding of very low frequencies, such as that of a deep bass note. That is because humans can hear frequencies as low as 20 Hz. The lowest sound frequencies are coded by frequency matching, whereby the frequency is matched by the firing rate of auditory nerve fibres. Low-to-moderate frequencies are coded by both frequency matching and the place on the basilar membrane at which the wave peaks. High frequencies are coded only by the place at which the wave peaks.
Volley theory
The view that some sounds are coded by matching the frequency of neural firing
Light is a form of energy known as:
Electromagnetic radiation. Most electromagnetic radiation (including X-rays, radio waves, television signals and radar) is invisible to the human eye. In fact, the range, or spectrum, of visible light is just the tiny slice of electromagnetic radiation whose wavelength is from just under 400 nanometres (nm) to about 750 nanometres (a nanometre is one-billionth of a metre).
Visible light
Is electromagnetic radiation that has a wavelength of approximately 400–750 nanometres
Sensations of light depend on two physical dimensions of light waves:
Intensity and wavelength.
Light intensity
Refers to how much energy the light contains; it determines the brightness of light, much as the amplitude of sound waves determines the loudness of sound.
Light wavelength
Is the distance between peaks in light waves. What colour you sense depends mainly on light wavelength. At a given intensity, different wavelengths produce sensations of different colours, much as different sound frequencies produce sensations of different pitch
Visual transduction
Occurs when light energy is transduced into nerve cell activity in the eye.
Process of focusing light
Before the transduction process occurs, accessory structures in the human eye modify incoming light rays. The light rays enter the eye by passing through a transparent, protective layer called the cornea. Then the light passes through the pupil, the opening just behind the cornea. The iris, which gives the eye its colour, adjusts the amount of light allowed into the eye by constricting to reduce the size of the pupil or relaxing to enlarge it. Directly behind the pupil is the lens. The cornea and the lens of the human eye are both curved so that, like the lens of a camera, they bend light rays. The light rays are focused into an image on the surface (retina) at the back of the eye. Light rays from the top of an object are focused at the bottom of the image on the retinal surface. Light rays from the right side of the object end up on the left side of the retinal image .The brain rearranges this upside-down and reversed image so that we can see the object as it is.
Cornea
The curved, transparent, protective layer through which light rays enter the eye.
Pupil
An opening in the eye, just behind the cornea, through which light passes.
Iris
The colourful part of the eye, which constricts or relaxes to adjust the amount of light entering the eye.
Lens
The part of the eye behind the pupil that bends light rays.
Retina
The surface at the back of the eye onto which the lens focuses light rays
Ocular accommodation
The ability of the lens to change its shape and bend light rays so that objects are in focus
In some older people, vision is impaired by
Cataracts, a condition in which a ‘cloudy’ lens severely reduces incoming light. Cataracts can be cleared up with laser surgery or by replacing the natural lens with an artificial one
You see objects as they are because your brain:
Rearranges the upside-down and reversed images that the lens focuses on the retina.
A common eye condition in younger people is:
Nearsightedness, in which close objects are in focus but distant ones are blurry. This condition is partly genetic but it may also be made more likely by environmental factors, such as when people spend more time looking at close-up images and less time far-gazing.
Photoreceptors
Are specialised cells in the retina that convert light energy into nerve cell activity. The photopigments: are chemicals in photoreceptors that respond to light and assist in converting light into nerve cell activity.
The eye has three major layers
The sclera: which s the white part of our eye which maintains, protects, and supports the shape of the eye and includes the cornea; The choroid, which provides oxygen and nourishment to the eye and includes the pupil, iris, and lens; and The retina, which allows us to piece images together and includes specialised cells such light receptors known as cones and rods.
Dark Adaptation
Is the increasing ability to see in the dark as time passes. In the dark, as your photoreceptors create more photopigments, your ability to see gradually increases. In fact, you become about 10 000 times more sensitive to light after about half an hour in a darkened room.
The retina has two main types of photoreceptors:
Rods and cones which differ in shape, but they also differ in their response to light.