Thresholds

• Absolute threshold, the weakest level of a stimulus that can be correctly detected at least half the time.

• According to signal detection theory, there is no actual absolute threshold because the threshold changes with a variety of factors, including fatigue, attention, expectations, motivation, and emotional distress.

• Subliminal stimulation is the receipt of messages that are below one’s absolute threshold for conscious awareness.

  • Subliminal messages can have a momentary, subtle effect on thinking.

• Difference threshold—the minimum difference between any two stimuli that a person can detect 50 percent of the time—has been reached.

• According to Weber’s law, which was quantified by Gustav Fechner, difference thresholds increase in proportion to the size of the stimulus.

• Sensory adaptation permits you to focus your attention on informative changes in your environment without being distracted by irrelevant data such as odors or background noises.

Transmission of Sensory Information

• Transduction refers to the transformation of stimulus energy to the electrochemical energy of neural impulses.

• Perception is the process of selecting, organizing, and interpreting sensations, enabling you to recognize meaningful objects and events.

Vision

• Since most people rely on sight, psychologists study visual perception.

• The retina's cones and rods, the brain's pathways, and the visual cortex in the occipital lobes are where visual sensation and perception begin.

• Your retinal image is upside-down and incomplete. Your brain instantly corrects the upside-down image.

Visual Pathway

• Millions of rods and cones are the photoreceptors that convert light energy to electrochemical neural impulses.

• Your eyeball is protected by an outer membrane composed of the sclera, tough, white, connective tissue that contains the opaque white of the eye, and the cornea, the transparent tissue in the front of your eye.

• Rays of light entering your eye are bent first by the curved transparent cornea, pass through the liquid aqueous humor and the hole through your muscular iris called the pupil, are further bent by the lens, and pass through your transparent vitreous humor before focusing on the rods and cones in the back of your eye.

• Nearsighted if too much curvature of the cornea and/or lens focuses an image in front of the Farsighted if too little curvature of the cornea and/or lens focuses the image behind the retina so distant objects are seen more clearly than nearby ones.

• Astigmatism is caused by an irregularity in the shape of the cornea and/or the lens.

• Dark adaptation:  When it suddenly becomes dark, your gradual increase in sensitivity to the low level of light

• Bipolar cells: Rods and cones both synapse with a second layer of neurons in front of them in your retina.

• Bipolar cells transmit impulses to another layer of neurons in front of them in your retina, the ganglion cells.

• Blind spot: Where the optic nerve exits the retina, there aren’t any rods or cones, so the part of an image that falls on your retina in that area is missing.

• Feature detectors:  The thalamus then routes information to the primary visual cortex of your brain, where specific neurons

• Parallel processing: Simultaneous processing of stimulus elements

Color Vision

• The colors of objects you see depend on the wavelengths of light reflected from those objects to your eyes.

• Light is the visible portion of the electromagnetic spectrum.

• The colors vary in wavelength from the longest (red) to the shortest (violet).

• A wavelength is the distance from the top of one wave to the top of the next wave.

• In the 1800s, Thomas Young and Hermann von Helmholtz accounted for color vision with the trichromatic theory that three different types of photoreceptors are each most sensitive to a different range of wavelengths.

• People with three different types of cones are called trichromats; with two different types, dichromats; and with only one, monochromats.

• People who are color-blind lack a chemical usually produced by one or more types of cones.

• According to Ewald Hering’s opponent-process theory, certain neurons can be either excited or inhibited, depending on the wavelength of light, and complementary wavelengths have opposite effects.

Hearing (Audition)

• Hearing is the primary sensory modality for human language.

• Amplitude is measured in logarithmic units of pressure called decibels (dB).

• Pitch: determine the highness or lowness of the sound

• You can tell the difference between the notes of the same pitch and loudness played on a flute and on a violin because of a difference in the purity of the wave form or mixture of the sound waves, a difference in timbre.

Ear

• The pinna, auditory canal, and tympanum make up your outer ear.

• The eardrum vibrates with sound waves from the outer ear.

• The middle ear's ossicles—the hammer, anvil, and stirrup—vibrate.

• The vibrating stirrup hits the inner ear's cochlea oval window.

• A basilar membrane with hair cells bends vibrations and converts them to neural impulses.

• Auditory neurons form the auditory nerve by synapsing with hair cells.

• The auditory nerve sends sound to the temporal lobe auditory cortex via the medulla, pons, and thalamus.

• The medulla and pons cross most auditory nerve fibers, so your auditory cortex receives input from both ears, but contralateral input dominates.

• The process by which you determine the location of a sound is called sound localization.

• According to Georg von Békésy’s place theory, the position on the basilar membrane at which waves reach their peak depends on the frequency of a tone.

• According to frequency theory, the rate of the neural impulses traveling up the auditory nerve matches the frequency of a tone, enabling you to sense its pitch.

• Conduction deafness is a loss of hearing that results when the eardrum is punctured or any of the ossicles lose their ability to vibrate.

• Nerve (sensorineural) deafness results from damage to the cochlea, hair cells, or auditory neurons.

• Somatosensation as a general term for four classes of tactile sensations: touch/pressure, warmth, cold, and pain.

• Itching results from repeated gentle stimulation of pain receptors, a tickle results from repeated stimulation of touch receptors, and the sensation of wetness results from simultaneous stimulation of adjacent cold and pressure receptors.

• Touch is necessary for normal development and promotes a sense of well-being.

• Ronald Melzack and Patrick Wall’s gate-control theory attempts to explain the experience of pain.

  • You experience pain only if the pain messages can pass through a gate in the spinal cord on their route to the brain.

Body Senses

• Kinesthesis is the system that enables you to sense the position and movement of individual parts of your body.

• Sensory receptors for kinesthesis are nerve endings in your muscles, tendons, and joints.

• Your vestibular sense is your sense of equilibrium or body orientation.

Chemical Senses

• Gustation (taste) and olfaction (smell) are called chemical senses because the stimuli are molecules.

• Your chemical senses are important systems for warning and attraction.

• You won’t eat rotten eggs or drink sour milk, and you can smell smoke before a sensitive household smoke detector.

• Taste receptor cells are most concentrated not only on your tongue in taste buds embedded in tissue called fungiform papillae, but are also on the roof of your mouth and the opening of your throat.

• Tasters have an average number of taste buds, nontasters have fewer taste buds, and supertasters have the most.

• Supertasters are more sensitive than others to bitter, spicy foods and alcohol, which they find unpleasant.

Attention

• Selective attention: You focus your awareness on only a limited aspect of all you are capable of experiencing.

• Bottom-up processing: your sensory receptors detect external stimulation and send these raw data to the brain for analysis.

• Top-down processing takes what you already know about particular stimulation, what you remember about the context in which it usually appears, and how you label and classify it, to give meaning to your perceptions.

• Visual capture:  Where you perceive a conflict among senses, vision usually dominates.

Gestalt Organizing Principles of Form Perception

• Max Wertheimer, Kurt Koffka, and Wolfgang Kohler studied how the mind organizes sensations into perceptions of meaningful patterns or forms, called a gestalt in German.

• Phi phenomenon, which is the illusion of movement created by presenting visual stimuli in rapid succession.

• Figure–ground relationship: The figure is the dominant object, and the ground is the natural and formless setting for the figure.

• Proximity, the nearness of objects to each other, is an organizing principle.

• Principle of closure states that we tend to fill in gaps in patterns.

  • The closure principle is not limited to vision.

• Principle of similarity states that like stimuli tend to be perceived as parts of the same pattern.

• Principle of continuity or continuation states that we tend to group stimuli into forms that follow continuous lines or patterns.

• Optical or visual illusions are discrepancies between the appearance of a visual stimulus and its physical reality.

• Visual illusions, such as reversible figures, illustrate the mind’s tendency to separate figure and ground in the absence of sufficient cues for deciding which is which.

Depth Perception

• Depth perception is the ability to judge the distance of objects.

• Monocular cues are clues about distance based on the image of one eye, whereas binocular cues are clues about distance requiring two eyes.

• Retinal disparity, which is the slightly different view the two eyes have of the same object because the eyes are a few centimeters apart.

• Motion parallax involves images of objects at different distances moving across the retina at different rates.

• Interposition or overlap can be seen when a closer object cuts off the view of part or all of a more distant one.

• Relative size of familiar objects provides a cue to their distance when the closer of two same-size objects casts a larger image on your retina than the farther one.

• Relative clarity can be seen when closer objects appear sharper than more distant, hazy objects.

• Texture gradient provides a cue to distance when closer objects have a coarser, more distinct texture than faraway objects that appear more densely packed or smooth.

• Relative height or elevation can be seen when the objects closest to the horizon appear to be the farthest from you.

• Linear perspective provides a cue to distance when parallel lines, such as edges of sidewalks, seem to converge in the distance.

• Relative brightness can be seen when the closer of two identical objects reflects more light to your eyes.

• Optical illusions, such as the Müller-Lyer illusion and the Ponzo illusion, in which two identical horizontal bars seems to differ in length, may occur because distance cues lead one line to be judged as farther away than the other.

Perceptual Constancy

• As a car approaches, you know that it’s not growing in size, even though the image it casts on your retina gets larger, because you impose stability on the constantly changing sensations you experience.

• Three perceptual constancies are size constancy,  by which an object appears to stay the same size despite changes in the size of the image it casts on the retina as it moves farther away or closer; shape constancy, by which an object appears to maintain its normal shape regardless of the angle from which it is viewed; and brightness constancy, by which an object maintains a particular level of brightness regardless of the amount of light reflected from it.

Perceptual Adaptation and Perceptual Set

• If you repeated your actions, you probably reached the item quickly.

• Blind people who become sighted can immediately distinguish colors and figure from ground, but it takes time to recognize shapes.

• Cultural assumptions and beliefs affect visual perception.

• You must be familiar with the object and have seen it in the distance to use relative size.

Culture and Experience

• Your perceptual set or mental predisposition can influence what you perceive when you look at ambiguous stimuli.

• Your perceptual set is determined by the schemas you form as a result of your experiences.

• Schemas are concepts or frameworks that organize and interpret information.