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Chapter 5

Chapter 5 Notes

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Psychology 1000

CHAPTER 5: SENSATION AND PERCEPTION - synesthesia: a condition where stimuli are experienced by more than one sense. Literally means mixing of the senses can experience sounds as colours or tastes as touch sensations that have different shapes - Sensory receptors must translate information into nerve impulses. Then, specialized neurons break down and analyze the specific features of the stimuli. At the next stage, these numerous stimulus pieces are reconstructed into a neural representation that is then compared with our knowledge of what particular objects look, smell, or feel like. This allows us to recognize the stimulus. - Sensation: the stimulus-detection process by which our sense organs respond to and translate environmental stimuli into nerve impulses that are sent to the brain - Perception: making sense of what our senses tell us the active process of organizing this stimulus input and giving it meaning > SENSORY PROCESSES - more than just the 5 classical senses vision, audition, touch, gustation (taste), and olfaction (smell) - also senses that provide info about balance and body position, pressure, pain, temperature, foreign invaders in the immune system, etc - psychophysics: studies relations between the physical characteristics of stimuli and sensory capabilities concerned with two types of sensitivity: absolute limits of sensitivity, and the differences between stimuli The Absolute Threshold: - asks how intense must a stimulus be before we can detect its presence? - researchers present stimuli of varying intensities and ask ppl if they can detect it - the absolute threshold: the lowest intensity at which a stimulus can be detected correctly 50% of the time (lower the absolute threshold, greater the sensitivity) Signal Detection Theory: - level of sensitivity for each sense can vary from person to person - can also vary based on factors such as fatigue, expectation, or potential significance of the stimulus - signal detection theory: concerned with the factors that influence sensory judgments - ask participants if they hear a tone 4 outcomes: hit, miss, false alarm, or correct rejection (figure 5.3 pg 162) - at low stimulus intensities, the decision criterion is influenced by both the participants and the situations characteristics bold participants say yes more than conservative participants, and manipulating the rewards or costs for correct or incorrect responses can put more pressure to answer correctly The Difference Threshold: - the smallest difference between two stimuli that ppl can perceive 50% of the time - also called the just noticeable difference (jnd) 1 - Webers law: the jnd is directly proportional to the magnitude of the stimulus with which the comparison is being made, and can be expressed as a Weber fraction Eg, the jnd value for weights is a Weber fraction of approx. 1/50 this means that if you lift a weight of 50 grams, a comparison weight must weigh at least 51 grams for you to be able to say it was heavier Does not work at extremely high and low intensities Table 5.2 pg 165 Sensory Adaptation - Sensory adaptation: sensory neurons are engineered to respond to a constant stimulus by decreasing their activity, and diminishing sensitivity to that stimulus (also known as habituation) - R.M. Pritchard demonstrated that if tiny involuntary eye movements did not keep images moving around the retina, stationary objects would fade from sight - Sensory adaptation allows us to pick up informative changes in the environment by freeing our senses from the constant and mundane stimuli around us > THE SENSORY SYSTEMS Vision - stimulus for vision is electromagnetic energy, or light waves, measured in nanometers (nm) humans can detect from about 700nm (red) to about 400nm (blue-violet) The Human Eye - light waves enter the eye through the cornea, a transparent protective structure at the front of the eye - Behind the cornea is the pupil, an adjustable opening that can dilate or constrict to control the amount of light that enters the eye. The pupils size is controlled by muscles in the coloured iris - Behind the pupil is the lens, an elastic structure that becomes thinner to focus on distant objects and thicker to focus on nearby objects - The lens focuses the visual image on the light-sensitive retina, a multi-layered tissue at the rear of the fluid-filled eyeball - Myopia (nearsightedness): the lens focuses the visual image in front of the retina, resulting in a blurred image for faraway objects. Usually occurs because the eyeball is longer than normal - Hyperopia (farsightedness): occurs when the lens does not thicken enough and the image is focused on a point behind the retina. Aging typically causes the eyeball to become shorter, which is why many older ppl need reading glasses Photoreceptors: Rods and Cones - the retina contains two types of light-sensitive receptor cells: rods and cones there are about 120 million rods and 6 million cones in the human eye 2- rods function best in dim light, and are primarily black-and-white brightness receptors. They are about 500 times more sensitive to light than cones, but cannot sense colour. - Cones are colour receptors, and function best in bright light - in humans, rods and cones are found throughout the retina except in the fovea, a small area in the center of the retina that contains only cones. Cones decrease in concentration as one moves away from the center of the retina - rods and cones send their msgs to the brain via bipolar cells and ganglion cells - bipolar cells have synaptic connections with the rods and cones, then they synapse with a layer of about one million ganglion cells, whose axons are collected into a bundle to form the optic nerve - Typically, many rods are connected to the same bipolar cell. They therefore can combine their individual electrical msgs to the bipolar cell, where the effect of the many signals may be enough to fire it. That is why we can detect a faint stimulus more easily if we look at it off to the side so that it does not fall on the fovea, but on the peripheral of the retina, where the rods are most dense - Cones in the fovea each have their own private line to a single bipolar cell, so our visual acuity, or ability to see fine detail, is best when an image is focused right on the fovea eagles and hawks have 2 fovea to allow them to see small prey - The optic nerve formed by the axons of the ganglion cells exits through the back of the eye producing a blind spot, where there are no photoreceptors we are unaware of the blin
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