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Sensation and perception

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University of Toronto Scarborough
Steve Joordens

Sensation and perception (chapter 4) - Synesthesia: the perceptual experience of one sense that is evoked by another sense Our senses encode the information our brains perceive - Sensation: simple stimulation of a sense organ, basic registration of light, sound, pressure, odor, taste - Perception: the organization, identification, and interpretation of a sensation in order to form a mental representation - Transduction: when many sensors in the body convert physical signals from the environment into encoded neural signals sent to the central nervous system Psychophysics - Wilhelm wundt and Edward titchner - Gustav Fechner, an approach to measure sensation and perception - Psychophysics: methods that measure the strength of a stimulus and the observer’s sensitivity to that stimulus Measuring thresholds Absolute threshold - Absolute threshold: the minimal intensity needed to just barely detect a stimulus, a boundary Difference thresholds - Useful for assessing how sensitive we are to faint stimuli - Just noticeable difference (JND): the minimal change is a stimulus that can just barely be detected - Ernst weber - Weber’s law: the just noticeable difference of a stimulus is a constant proportion despite variations in intensity - It is the proportion between stimuli that is important, the measured size of the difference, whether in brightness, loudness, weight irrelevant Signal detection - Sensory signals face a lot of competition, noise, which refers to all the other stimuli coming from the internal and external environment - Signal detection theory: the response to a stimulus depends both on a person’s sensitivity to the stimulus in the presence of noise and on a person’s decision criterion - P. 131 outcomes - Proposes a way to measure perceptual sensitivity Sensory adaptation - Sensory adaptation: sensitivity to prolonged stimulation tends to decline over time as an organism adapts to current conditions - Change in responding to sensory events - Respond more strongly to changes in stimulation than to constant stimulation Vision I: how the eyes and the brain convert light waves to neural signals - Visual acuity: the ability to see fine detail, the smallest line of letters that a typical person can read from a distance of 20 feet Sensing light - Visible light is simply the portion of the electromagnetic spectrum that we can see - Length, amplitude, purity The human eye - Cornea, iris, pupil - Retina: light sensitive tissue lining the back of the eyeball - Accommodation: the process by which the eye maintains a clear image on the retina - Eyeball too long, nearsightedness (myopia) - Eyeball too short, farsightedness (hyperopia) Phototransduction in the retina - Photoreceptor cells - Cones: detect colour, operate under normal daylight conditions, and allow us to focus on fine detail - Rods: become active under low light conditions for night vision - Fovea: an area of the retina where vision is the clearest and there are no rods at all - Peripheral vision - Bipolar cells collect neural signs from the rods and comes and transmit them to the outermost layer of the retina, where neurons called retinal ganglion cells organize the signals and send them to the brain - Optic nerve - Blind spot: a location in the visual field that produces no sensation on the retina Receptive fields - Receptive field: the region of the sensory surface that, when stimulated, causes a change in the firing rate of that neuron Perceiving colour Seeing colour - Isaac newton colour is nothing but our perception of wavelengths - The rainbow of hues and accompanying wavelengths is called the visible spectrum - A white surface really is reflecting all visible wavelengths of light, increasing light to create colour in this way is called additive colour mixing - Darker colour, reflect less light Trichromatic colour representations in the cones - Respond to short wavelengths (bluish) - Medium wavelengths (greenish) - Long wavelengths (reddish) - Trichromatic colour representation: the pattern of responding across the three types of cones provides a unique code for each colour - Colour deficiency/ colour blindness Colour opponent representation into the brain - Staring too long at one colour fatigues the cones that respond to that colour, producing a form of sensory adaptation that results in a colour afterimage - Colour opponent system: pairs of visual neurons work in opposition- red against green, blue against yellow The visual brain - Optic nerve travels to each eye to the lateral geniculate nucleus, in the thalamus - Area v1: the part of the occipital lobe that contains the primary visual cortex Neutral systems for perceiving shape Pathways for what, where, and how - Visual form agnosia: the inability to recognize objects by sight Vision II: recognizing what we perceive Attention: the glue that binds individual features into a whole - Binding problem: ho
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