College of Education

School of Continuing and Distance Education 2014/2015 – 2016/2017

PSYC 221

Introduction to General

Psychology

Session 3 – Sensation and perception

Lecturer: Dr. Joana Salifu Yendork, Psychology Department Contact Information: jyendork@ug.edu.gh

Session Overview

• As human, we always encounter stimuli but we hardly pay attention to the processes that go into the sensation and interpretation of these stimuli. A branch of psychology specializes in the understanding of sensation and perception. In this session, we will focus on how different sensation is from perception, the different modalities of sensation and perception, the different forms of perception and illusions.

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Session Outline

The key topics to be covered in the session are as follows:

• Defining and differentiating sensation and perception

• Sense organs and sensation

• Perception

• Visual illusions and perceptual problems

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Reading List

• Chapter 3 of Feldman (2007), Essentials of Understanding Psychology

• Chapter 5 of Myer (2008), Exploring psychology

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DEFINING AND DIFFERENTIATING SENSATION AND PERCEPTION

Topic One

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Defining and differentiating sensation

and perception • Sensation is the process by which our sense receptors and

nervous system receive and represent stimulus energies (Myers, 2008)

• Sensation is when we represent the world through detecting physical energy (a stimulus) from the environment and convert it into neural signals.

• occurs when energy in the external environment or the body stimulates receptors in the sense organs.

• Perception is the process of organizing and interpreting sensory information, thus enabling us to recognize meaningful objects and events (Myers, 2008).

• Perception is when we select, organize, and interpret our sensations

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SENSE ORGANS AND SENSATION

Topic Two

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Basic principles of sensation

• Thresholds • Absolute Threshold

– the minimum stimulation necessary to detect a particular light, sound, pressure, taste, or odor 50 percent of the time

• Vision: A single candle flame from 30 miles on a clear night

• Hearing: The tick of a watch from 20 feet in total quiet • Smell: One drop of perfume in a 6-room apartment • Touch: The wing of a bee on the cheek, dropped from 1

cm • Taste: One teaspoon of sugar in 2 gallons of water

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Basic principles of sensing

• To function effectively, we need absolute thresholds low enough to allow us to detect important sights, sounds, textures, tastes, and smells. We also need to detect small differences among stimuli.

• Difference threshold – The smallest difference in stimulation that a person can be

reliably detected when two stimuli are compared; also called Just Noticeable Difference (JND).

– E.g., detecting the difference if you add 1 spoon full of salt to food

• Signal-Detection Theory – Holds that responses in a detection task depend on a sensory

process and a decision process. Responses may vary with a person’s motivation, alertness, and expectations

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Basic principles of sensing

• Sensory Adaptation: The reduction or disappearance of sensory responsiveness that occurs when stimulation is unchanging or repetitious.

• Sensory Deprivation: The absence of normal levels of sensory stimulation.

• Selective Attention: The focusing of attention on selected aspects of the environment and the blocking out of others.

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Basic principles of sensing

• Bottom-up processing: here the analysis of stimulus begins with the sense receptors and work up to the level of the brain and mind

• Top-down processing: Here the information processing is guided by higher-level mental processes as the individual construct perceptions, draw on experience and expectation

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Sensory modalities

• Vision – The Stimulus Input: Light Energy

– Organ: The Eye

• Hearing – The Stimulus Input: Light Energy

– Organ: The Eye

• Others: – Touch

– Pain

– Taste

– Smell

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Psychophysics

• A study of the relationship between physical characteristics of stimuli and our psychological experience with them.

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Physical World Psychological World

Light Brightness

Sound Volume

Pressure Weight

Sugar Sweet

Vision

• For sensation to occur, the sense organs must transform the stimulus energy (sights, sounds, smells) into neural impulses.

• This process is called transduction.

• For the eyes to sense, it must transform light into neural impulses

• Light has the following characteristics: – Wavelength (hue/color):

• Hue/color is the dimension of color determined by the wavelength of the light.

• Wavelength is the distance from the peak of one wave to the peak of the next.

– Intensity (brightness): Amount of energy in a wave determined by the amplitude. It is related to perceived brightness.

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Vision

• Structures of the Human Eye:

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The eye

• Cornea: Transparent tissue where light enters the eye.

• Iris: Muscle that expands and contracts to change the size of the opening (pupil) for light.

• Lens: Focuses the light rays on the retina.

• Retina: Contains sensory receptors that process visual information and sends it to the brain.

• Lens: Transparent structure behind the pupil that changes shape to focus images on the retina.

• Accommodation: The process by which the eye’s lens changes shape to help focus near or far objects on the retina.

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The eye

• Retina: The light-sensitive inner surface of the eye, containing receptor rods and cones in addition to layers of other neurons (bipolar, ganglion cells) that process visual information.

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The eye

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• Optic nerve: Carries neural impulses from the eye to the brain.

• Blind Spot: Point where the optic nerve leaves the eye because there are no receptor cells located there.

• Fovea: Central point in the retina around which the eye’s cones cluster

Visual Information Processing

• Light enters the eye through the cornea, which protects the eye and bends light to provide focus

• The light then passes through the pupil, a small adjustable opening surrounded by the iris, a colored muscle that adjusts light intake.

• The iris dilates or constricts in response to light intensity and even to inner emotions.

• Behind the pupil is a lens that focuses incoming light rays into an image on the retina, a multilayered tissue on the eyeball’s sensitive inner surface. The lens focuses the rays by changing its curvature in a process called accommodation.

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Visual Information Processing

• How does the brain process visual information?

• Optic nerves connect to the thalamus in the middle of the brain, and the thalamus connects to the visual cortex.

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Visual Information Processing

• Processing of several aspects of the stimulus simultaneously is called parallel processing. The brain divides a visual scene into subdivisions such as color, depth, form, movement, etc.

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Visual information processing

• Gestalt principles describe the brain’s organization of sensory building blocks into meaningful units and patterns.

• The German word “Gestalt” roughly means to "whole" or "form"

• “The whole is greater than the sum of its parts.” • In order to interpret what we receive through our

senses, we attempt to organize this information into certain groups.

– Sense of shape: derived from the whole, not the sum of its parts

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Color vision

• T. Young (1802) & H. von Helmholtz (1852) both proposed that the eye detects 3 primary colors (red, blue, & green)

• All other colors can be derived by combining the activity of these three types of cones

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Hearing

• Stimulus input: sound waves – Sound waves are compressing and expanding air molecules.

• Sound characteristics: • Intensity (Loudness): Amount of energy in a wave,

determined by the amplitude, relates to the perceived loudness.

• Frequency (pitch): The dimension of frequency determined by the wavelength of sound.

• Wavelength: The distance from the peak of one wave to the peak of the next.

• Timbre: The distinguishing quality of sound; the dimension of auditory experience related to the complexity of the pressure wave.

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How does the ear transmit sound energy into neural messages?

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The Ear

•To understand how the ear transmit sound energy into neural messages, you have to understand the parts of the ears and their function. •Outer Ear: Collects and sends sounds to the eardrum. •Middle Ear: Chamber between eardrum and cochlea containing three tiny bones (hammer, anvil, stirrup) that concentrate the vibrations of the eardrum on the cochlea’s oval window. •Inner Ear: Innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs. •Cochlea: Coiled, bony, fluid-filled tube in the inner ear that transforms sound vibrations to auditory signals.

Other sense organs

• Taste:

• Papillae: Knoblike elevations on the tongue, containing the taste buds (Singular: papilla).

• Taste buds: Nests of taste-receptor cells.

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Taste

• Taste sensations consisted of sweet, salty, sour, and bitter tastes.

• Recently, receptors for a fifth taste have been discovered called “Umami”.

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Smell: the sense of smell

• Airborne chemical molecules enter the nose and circulate through the nasal cavity.

• Receptors on the roof of the nasal cavity detect these molecules.

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Senses of the Skin

• Touch :The sense of touch is a mix of four distinct skin senses—pressure, warmth, cold, and pain.

• Only pressure has identifiable receptors. All other skin sensations are variations of pressure, warmth, cold and pain.

• Pain tells the body that something has gone wrong. Usually pain results from damage to the skin and other tissues. A rare disease exists in which the afflicted person feels no pain.

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PERCEPTION Topic Three

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Perceptual organisation

• How do we form meaningful perceptions from sensory information?

• How did the Gestalt psychologists understand perceptual organization?

• According Gestalt psychologists, we make meaning of sensations by organising them

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Gestalt principles of organization

• Perceptual parsing:

– Segregating the “scene” into its constituent objects

– The first step to organizing

• Gestalt principles of organization:

• Issues of figure/ground

• Similarity

• Proximity

• Good continuation

–“subjective contours”

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Gestalt principles of organisation

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Gestalt principles of organization

–Form perception: Is the object figure or ground?

• Our interpretation of figure / ground will influence how we perceive an object

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Gestalt psychology: figure-ground

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Depth perception

• Depth perception enable us to judge distances

• Two broad cues are use in our judgment of depth

• Binocular Cues: Visual cues to depth or distance that require the use of both eyes.

– Retinal disparity: Images from the two eyes differ.

– Convergence: Turning inward of the eyes, which occurs when they focus on a nearby object

– Retinal Disparity: The slight difference in lateral separation between two objects as seen by the left eye and the right eye.

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Depth perception • Monocular Cues: Visual cues to depth or distance that can be

used by one eye alone. – Relative Size: If two objects are similar in size, we perceive the one that

casts a smaller retinal image to be farther away – Interposition: Objects that occlude (block) other objects tend to be

perceived as closer. – Relative Height: We perceive objects that are higher in our field of vision to

be farther away than those that are lower. – Relative motion: Objects closer to a fixation point move faster and in

opposing direction to those objects that are farther away from a fixation point, moving slower and in the same direction.

– Linear Perspective: Parallel lines, such as railroad tracks, appear to converge in the distance. The more the lines converge, the greater their perceived distance.

– Light and Shadow: Nearby objects reflect more light into our eyes than more distant objects. Given two identical objects, the dimmer one appears to be farther away.

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Perceptual constancies

• The accurate perception of objects as stable or unchanged despite changes in the sensory patterns they produce. – Shape constancy

– Location constancy

– Size-distance constancy: distance cues help objects farther to appear bigger than those closer

– Brightness constancy

– Color constancy: Perceiving familiar objects as having consistent color even when changing illumination filters the light reflected by the object.

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Perceptual interpretation

• How important is experience in shaping our perceptual interpretation?

• Theorists have propounded explanations as to how we make meaning of the stimuli we encounter

• Immanuel Kant (1724-1804) maintained that knowledge comes from our inborn ways of organizing sensory experiences.

• John Locke (1632-1704) argued that we learn to perceive the world through our experiences.

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Findings from research

• After cataract surgery, blind adults were able to regain sight. These individuals could differentiate figure and ground relationships, yet they had difficulty distinguishing a circle and a triangle (Von Senden, 1932).

• After blind adults regained sight, they were able to recognize distinct features, but were unable to recognize faces. Normal observers also show difficulty in facial recognition when the lower half of the pictures are changed.

• Kittens raised without exposure to horizontal lines later had difficulty perceiving horizontal bars.

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Classical approach to perception

• Emphasis on the active, constructive role of the perceiver, who routinely:

– Resolves ambiguous figures

– Determines identity of objects based on contextual clues and previous knowledge

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Can you identify the phrase?

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ILLUSION AND PERCEPTUAL PROBLEMS

Topic Four

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Visual illusions

• Cues sometimes cause an over-estimate or under-estimate;

• Slight over/under interpretations can cause us to misinterpret the information we receive

• Usually: – perceptions are accurate

– are based on relevant experience

– reflect the world we live in

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What do you see?

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Perceptual problems

• Colour blindness: Genetic disorder in which people are blind to green or red colors. This supports the Trichromatic theory.

• Ishihara test

• Individuals who suffer from colour blindness can identify the number in the picture

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Sample Question

• Describe how the eyes and ears sense stimuli.

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References

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