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PSYA01H3 Chapter Notes -Superior Rectus Muscle, Superior Oblique Muscle, Cornea

Course Code
Steve Joordens

of 12
PSYA01H3 2010-11-24
Sensory Processing
x Sensation: the detection of the simple properties of a stimulus
x Perception: the detection of the more-complex properties of a stimulus, including its location and nature
¾ Includes both animate and inanimate objects, as well as their backgrounds and movements
x According to the above definitions, seeing the colour red is a sens. and recognizing a red apple is perc.
x Traditionally there are five named senses, however, there are many more in reality
x The task of the sense organs is to transmit signals to the brain that are coded in such a way as to represent
certain features of events that have occurred in the environment
x The task of the brain is so analyze this information and decide what has occurred
x Transduction: the process by which the sense organs convert energy from environmental events (physical
stimulus) into neural activity (the activity of receptor cells of sensory organs)
x Receptor cell: a neuron that directly responds to a physical stimulus, such as a light, vibrations, or aromatic
x In the somatosenses, dendrites of neurons respond directly to physical stimuli without the intervention of
specialized receptor cellsvhowever, some of these neurons have specialized endings that enable them to
respond to particular kinds of sensory information
x Types of energy transduction: radiant energy, mechanical energy, recognition of molecular shape, thermal
energy, chemical energy
x A code is a system of signals representing information Æ as long as we know the rules of a code, we can
convert a message from one medium to another without losing any information
x Anatomical coding: a means by which the nervous system represents information; different features are
coded by the activity of different neurons
¾ Interprets the location and type of sensory stimulus by which incoming nerve fibres are active
¾ Allows the brain to distinguish among stimuli of the same and well as different sensory modalities
x Temporal coding: a means by which the nervous system represents information; different features are
coded by the pattern of activity of neurons (in terms of time)
¾ The rate at which neurons are fired determines the intensity of the stimulation
x Psychophysics: a branch of psychology that measures the quantitative relation between physical stimuli
and perceptual experience
PSYA01H3 2010-11-24
x vt[just-noticeable-difference (jnd): the smallest difference between two similar stimuli that
can be distinguishedva.k.a. difference threshold
¾ The jnd is directly related to the magnitude of the existing stimulus
¾ Weber fractions: the ratio between a just-noticeable difference and the magnitude of a stimulus;
reasonably constant over the middle range of most stimulus intensities
x Gustav Fechner, German physiologist, measured the absolute magnitude of perceptual experience in jnds
x Threshold: the point at which a stimulus, or a change in the value of a stimulus, can just be detected
x Difference threshold: another name for just-noticeable-difference; the minimum detectable difference
between two stimuli
¾ The point at which the difference is detected 50% of the time
x Absolute threshold: the minimum intensity of a stimulus that can be detected (discriminated from no diff)
¾ The point at which a participant detects the stimulus 50% of the time
x Signal-detection theory: a mathematical theory of the detection of stimuli, which involves discriminating a
detecting the signal
¾ }v]}v]v}o[Á]oo]vPv}}]vP]Pvo
¾ Hits and negatives are positive; misses and false alarms are negative
¾ /v}}Àv}o[}v]((]vPZ]ZZ}o}(]}vUZs
purposely manipulate this bias
¾ Receiver-operating-characteristic curve (ROC curve): a graph of hits and false alarms of subjects
Detectability is measured by the relative distance of the curves from a 45o line
¾ dZÁ}u]v}v[v]]À]Ç}Z}µv}(]µostimulus
¾ Emphasizes that perceptual experience involves factors other than the activity of the sensory
systems, factors such as motivation and prior experience
Details of the Human Eye
x The eye is sensitive to light; a radiant energy similar to radio waves that oscillates as it is transmitted from
its sourcevthe wavelength is the distance between adjacent waves of radiant energy
¾ dZµo]uv]}v}(]À]]}v[u}o}oÇ}]}v}ÁÀovPZ
x The entire spectrum of wavelengths is known as the electromagnetic spectrumvthe part our eyes can
detect (the part we see as light) is known as the visible spectrum
PSYA01H3 2010-11-24
x Cornea: the transparent tissue covering the front of the eye; forms a bulge at the front of the eye and
admits light into the eye
x ScleraWZ}µPZ}µoÇ}(ZÇVZ^ÁZ]_}(ZÇ
x Iris: the pigmented muscle of the eyes ; consists of two bands of muscles that control the amount of light
admitted into the eye by controlling the size of the pupil
x The space behind the cornea is filled with aqueous fluids that are constantly being produced by tissue
behind the corner that filters the fluid from the bloodvit nourishes the cornea and other portions of the
front of the eye
x Lens: the transparent organ situated behind the iris of the eye; helps focus an image on the retina
¾ A special set of muscles, the ciliary muscles, can alter the shape of the lens so that images of either
nearby or distant objects can be focused on the retinavthis is known as accommodation
x Retina: the tissue at the back inside surface of the eye that contains the photoreceptors and associated
neuronsvperforms the sensory functions of the eye
¾ Has images focused on it upside down and reversed from left to right; the brain compensates for
this image alteration and appropriately interprets the information
x Usually, the length of the eye is just right to focus the image on the retina in sharp detailvhowever, some
x As people get older, their lens hardens and becomes less flexiblevrequiring them to get additional lens to
make up for the inability to focus on close objects (convex lens in reading glasses or bifocals w glasses)
x Photoreceptor: a specialized neuron (receptive cell) for vision in the retina; a rod or cone
¾ Transduces light into neural activity and sends information to neurons that send axons towards
one point at the back of the eyevthe optic disk
x Optic disk: a circular structure located at the exit point of the axons from the retina to the ganglion cells
that form the optic nerve, which connects to the human brain