Sensation and Perception PSYCHOLOGY – SSC 210 Sensation and Perception Zahbia Sarfraz Lahore School of Economics

Who is on top? The people pointing over the fence or the people on the ladder?

Sensation and Perception Receiving information from the outside world, translating and transmitting it to the brain. Perception Organizing and interpreting information received from the outside world. Stimulus Any aspect of the outside world that influences behavior or conscious experience

Sensation and Perception Energy from stimuli cannot go directly to the brain Sensory messages must be translated into neural impulses that neurons can carry and the brain understands Transduction: translation of one form of energy into another Sense organs transduce sensory energy into neural energy.

Sensory Limits Absolute threshold: the smallest magnitude of a stimulus that can be detected Difference threshold: the smallest difference between two stimuli that can be detected Sensory adaptation: weakened magnitude of a sensation resulting from prolonged presentation of the stimulus.

Sensation and Perception Psychophysics Study of the relationship between stimuli and our psychological response to them

Sense of Touch Pain Pain serves a function – it warns us of impending danger Endorphins Neurotransmitters in the brain that have a pain-killing effect Gate-control theory Nervous system can process limited number of sensory signals at once When the system is ‘full’ a neural gate in spinal cord blocks upward passage of additional signals to the brain You can partially shut the gate on pain by creating competing sensations

Perception What we perceive is often based more on how sensory information is processed in our brain rather than what is in front of our eyes Raw visual sensations are useless to us until they are organized Fundamental ways of perceptual organization: Gestalt psychologists

Gestalt Principles of Perception

Gestalt Principles of Perception Figure-ground when we see a visual stimulus, part of what we see is the center of our attention, i.e. the figure, whereas the rest is the indistinct ground.

Gestalt Principles of Perception Continuity We tend to perceive lines or patterns that follow a smooth curve as being part of a single unit. Gestalt law states that learners tend to continue shapes beyond their ending points In this example we are more likely to perceive the lines as two crossed lines instead of four meeting at the center.

Gestalt Principles of Perception Proximity Things that are close together are usually perceived as belonging together. The proximity principle holds that the closer objects are to another, the more likely they are to be perceived as a unit. The lines at the bottom of the page are more likely to be perceived as rows rather than as columns because they are nearer to one another horizontally than vertically.

Gestalt Principles of Perception Similarity Marks that look alike tend to be grouped together The similarity principle holds that objects that are similar in shape, size, color, or any other feature tend to be grouped together. So the dots form perceptual columns rather than rows because of the similarities in color.

Gestalt Principles of Perception Closure Incomplete figures of familiar things tend to be perceived as complete wholes. Again, we fill in missing sensory information to create complete and whole perceptions. The closure principle holds that where there are gaps in a pattern that resembles a familiar form, people mentally ‘close’ the gaps and perceive the object as whole. This tendency enables us to recognize imperfect representations in hand drawings, written material, and so on.

Perceptual Constancy The image of an object on your retina can vary in size, shape, and brightness But we still continue to perceive the object as stable in size, shape and brightness (i) Size constancy The tendency to view an object as constant in size despite changes in the size of its image on the retina (as we move) (ii) Shape constancy The tendency to see an object as retaining its form despite changes in orientation Size constancy: If you see a car from a block away, you still perceive its size not to change even though the image is smaller on your retina compared to a car parked right next to you. Shape constancy: You perceive a book to maintain its rectangular shape even though at the different angles, your retinal image of the book is not a rectangle.

Size Constancy

Perceptual Constancy (iii) Brightness constancy (iv) Color constancy The tendency to view an object’s brightness as the same irrespective of whether it is in a dimly lit room or a bright room even though the intensity of light reaching the eye changes considerably. (iv) Color constancy The tendency to see an object’s color as the same irrespective of the conditions of the light and surroundings that change incoming visual information

Motivation, Emotion & Perception Many psychological factors influence perception E.g. hunger, anxiety Indicates there is not a one to one relationship between a physical stimulus and what we perceive