Sensation and Perception

Basic Concepts of SensationSensation is the process by which physical stimuli that impinge on our sensory organs are converted into neural impulses that the brain uses to create our experiences of vision, touch, hearing, taste, smell, etc.Sensory receptors – Are specialized cells that detect sensory stimuli and convert them into neural impulsesPsychophysics – Is the study of how physical sources of stimulation - light, sound, odors, and etc. relate to our experience of these stimuli in the form of sensations.

Sensory ReceptorsSensory receptors are remarkably sensitive to certain types of stimuli. Absolute threshold – Is the smallest amount of a stimulus that a person can reliably detect 50% of the time. See Table 3.1 for clarification.Difference threshold - Is the minimal difference between two stimuli that people can reliably detect.Ernst Weber (Weber’s Law) – put forth that the amount you must change a stimulus to detect a difference is given by a constant fraction or proportion (called a constant) of the original stimulus. See Table 3.2

Signal Detection

Signal-detection theory – states that the threshold for detecting a signal depends not only on the properties of the stimulus itself, but also on the level of back ground stimulation, or noise, and on the biological and psychological characteristics of the perceiver. Levels of fatigue also contribute to signal detection; how well you are listening at this moment.

Sensory AdaptationThrough the process of sensory adaptation, sensory systems become less sensitive to constant or unchanging stimuli.VISION: SEEING THE LIGHT – Vision is the process by which light energy is converted into signals (neural impulses) that the brain interprets to produce the experience of sight.LIGHT: THE ENERGY OF VISION – Light is _____________ energy in the form of electromagnetic radiation (electrically charged particles). Visible light occupies only a small portion of the range of electromagnetic radiation that is called the electromagnetic spectrum. See Figure 3.1. Different wavelengths within the visible spectrum give rise to the experience of different colors.

The Eye: The Visionary Sensory Organ

The _____________ is the organ with receptor cells that respond to light. Light enters the eye through the ________. A muscle called the ___________ contracts or expands to determine the amount of light that enters. The _________ of the eye is the black opening inside the iris. _____________ is the name of the process by which the lens changes its shape to focus images more clearly on the retina.The retina contains two kinds of photoreceptors (light sensitive cells, e.g., rods and cones) that are sensitive to light.

Photoreceptors- Part 1Rods and cones convert the physical energy of light into __________ signals that the brain processes to create visual sensations.The ______ in your eye are responsible for your peripheral vision.The neural signals produced by the photoreceptors pass back through a layer of interconnecting cells called bipolar cells and then through a layer of neurons called_________ cells. The ____________ nerve, which contain millions of ganglion axons, transmits visual information to the visual cortex which lies in the occipital lobes.

Photoreceptors – Part 2

What is a blind spot?What is a fovea? Feature detectors – Are specialized neurons in the visual cortex that respond only to particular features of visual stimuli, such as horizontal or vertical lines.COLOR VISION – Hermann von Helmholtz proposed a theory of color known as the trichromatic theory, which states that our ability to see different colors depends on the relative activity of three types of color receptors in the eye (red, green, and blue-violet).What is afterimage?

Opponent-process theory – suggests that the eyes have three types of color receptors; however, each color receptor consists of a pair of opposing receptors. Rather than having three separate receptors for red, green, and blue-violet, some receptors are sensitive to red or green; others to blue or yellow; and others, to black or white.What are trichromats?What are monochromats?What are dichromats?

Hearing – The Mechanics

We hear by sensing sound waves, which result from changes in the ____________ of air or water. When sound waves impinge upon the ear, they cause parts of the ear to __________. These vibrations are then converted into _________________ signals that are sent to the brain.

Sound: Sensing Waves of Vibrations

Unlike light that can travel through emptiness, sound exists only in a medium, such as air, liquids, gases, or solids. Vibrations are characterized by such physical properties as amplitude (the height of the wave, which is a measure of the amount of energy in the sound wave) and frequency (the number of complete waves, or cycles, per second). The amplitude of sound waves determines their perceived loudness and is measured in decibels.

The Ear: A Sound MachineThe outer ear funnels sound waves to the __________, a tight membrane that vibrates in response to them. The vibrations are then transmitted through three tiny bones in the middle ear called the ____________. The vibration is then transmitted to the oval window. The oval window connects the middle ear to the ___________. The vibration inside the cochlea, causes the basilar membrane to vibrate. The basilar membrane is attached to a gelatinous structure called the organ of Corti, which is lined with hair cells that serve as auditory ______________. The message is then received by the auditory cortex, which is located in the temporal lobes of the cerebral cortex.

Perception of Pitch – Perceiving the Highs and Lows

Place Theory – suggests that people perceive a sound to have a certain pitch according to the place along the basilar membrane that vibrates the most when sound waves of particular frequencies strike the ear.Frequency Theory – the belief that pitch depends on the frequency of vibration of the basilar membrane and the volley of neural impulses transmitted to the brain via the auditory nerve.Volley Principle – The principle that relates the experience of pitch to the alternating firing of groups of neurons along the basilar membrane.

Protecting your hearing

Conduction deafness – Refers to a form of deafness, usually involving damage to the middle ear, in which there is a loss of conduction of sound vibrations through the ear.Nerve deafness – Refers to deafness associated with nerve damage, usually involving damage to the hair ells or the auditory nerve itself.

Olfaction: What Your Nose KnowsStimulation of the sense of smell depends on the shape of the molecules of chemical substances. Smell is the only sense in which sensory information does not go through the thalamus on its way to the cerebral cortex. Olfactory information travels through the olfactory nerve directly to the olfactory bulb, a structure in the front of the brain above the nostrils. This information is then routed to the olfactory cortex in the temporal lobe and to several structures in the limbic system. Many species emit chemical substances called pheromones that play important roles in attracting mates, marking territory, controlling aggression, and organizing food-gathering efforts.

Taste: The Flavorful SenseLike the sense of smell, the sense of taste depends on receptors that detect chemical substances and transmit information about them to the brain. The receptors are called taste cells. These are nerve cells located within pores or openings on the tongue called taste buds.THE SKIN SENSES: YOUR LARGEST SENSORY ORGAN –Your skin contains receptors for the body’s skin senses that code for sensations of touch pressure. The sensory receptors transmit sensory information to the spinal cord, which relays it to the somatosensory cortex, the part of the cerebral cortex that processes information making us aware of how and where we have been touched.Pain receptors are located throughout the body.

Gate-Control Theory of PainAccording to the gate-control theory of pain, a gating mechanism in the spinal cord opens and closes to let pain messages through to the brain or to shut them out. The term “gate” is a pattern of nervous system activity that results in either blocking pain signals or letting them through.Endorphins – Are neurotransmitters that are similar in chemical composition to narcotic drugs, such as heroin, that have painkilling effects.Acupuncture – Is an ancient Chinese practice of inserting and rotating thin needles in various parts of the body in order to release natural healing energy.

The Kinesthetic and Vestibular Senses: Of Grace and Balance

This is the sense that keeps up informed about movement of the parts of the body and their position in relation to each other is called____________.The vestibular sense is the sensory system that monitors the position of your body in space and helps you maintain your balance.Organs in the inner ear that connect the semicircular canals are called___________.The three curved tube-like canals in the inner ear that are involved in sensing changes in the direction and movement of the head is called_____________.

Perceiving our World: Perception vs. Reality

Perception is the process by which the brain interprets sensory information, turning it into meaningful representations of the external world.The first step in perception is giving attention.Selective attention - Is the process by which we attend to meaningful stimuli and filter out irrelevant or extraneous stimuli.Habituation is the reduction in the strength of a response to a constant or repeated stimulus.Perceptual set is the tendency for our perceptions to be influenced by expectations or preconceptions. See fig. 3.17

Processing Bottom-Up or Top-Down

Bottom-up processing is a mode of perceptual processing by which the brain recognizes meaningful patterns by piecing together its and pieces of sensory information.Top-down processing is a mode of perceptual processing by which the brain identifies patterns as meaningful wholes rather than as piecemeal constructions.Proximity is the principle that objects that are near each other will be perceived as belonging too a common set.Similarity is the principle that objects that are similar will be perceived as belonging to the same group.

Laws of perceptual organization

Laws of perceptual organization identifies principles by gestalt psychologists that describe the way in which the brain groups bits of sensory stimulation into meaningful wholes or patterns, e.g., figure – ground perception and laws of grouping.Figure-ground perceptions- Refers to how we see figures and the background against which the figures are perceived serves as the ground. See figure 3.20

Laws of GroupingContinuity- Is a tendency to perceive a series of stimuli as a unified form when the stimuli appear to represent a continuous pattern. Fig. 3.23cClosure- the perceptual principle that people tend to piece together disconnected bits of information to perceive whole forms. Connectedness- Our tendency to perceive objects as belonging together when they are positioned together or are moving together.Perceptual constancy- The tendency to perceive an object as having the same shape despite differences in the images it casts on the retina as the viewer’s perspective changes, e.g., shape constancy

Examples of Perceptual Constancy

Shape constancy- The tendency to perceive an object as having the same shape despite differences in the images it casts on the retina.Size constancy- The tendency to perceive an object as having the same size…Color constancy- The tendency to perceive an object as having the same color despite changes in lighting conditions.Brightness constancy- The tendency to perceive objects as retaining their brightness even when they are viewed in dim light.

Cues to Depth PerceptionBinocular Cues for Depth- Cues for depth that involve both eyes. Because each eye receives slightly different images of the world, the brain interprets the difference in the two retinal images as cues to the relative distances of objects. Retinal disparity- Is the binocular cue for distance based on the slight differences in the visual impressions formed in both eyes.Convergence- Refers to the degree of tension required to focus two eyes on the same object.Monocular cues- Refer to cues for depth that can be perceived by each eye alone, such as relative size and interposition.

Visual Illusions: Do Your Eyes Deceive You?

Visual illusions- Are misperceptions of visual stimuli, e.g., Muller-Lyer Illusion and Ponzo illusion, See fig. 3.27.Carpentered-world hypothesis- Is an attempt to explain the Muller-Lyer illusion in terms of the cultural experience of living in a carpentered, right-angled world like our own.Paranormal phenomena- events that cannot be explained by known physical, psychological, or biological mechanisms. The study of such events is known as parapsychology.The EndSTUDY STUDY STUDY