Chapter 5: Sensation and Perception

Energy Senses

Vision

• Vision is the dominant sense in human beings.
• Sighted people use vision to gather information about their environment more than any other sense.

Step One: Gathering Light

• Several factors affect color perception.
• Light intensity - It indicates light energy.
  • This affects brightness.
  • Light wavelength determines hue.
• Infrared, microwave, and radio waves exceed visible light.
• UV and X-rays are shorter than visible light.

Step Two: Within the Eye

• The reflected light first enters the eye through the cornea, a protective covering.
• Then the light goes through the pupil.
• The muscles that control the pupil (called the iris) open it (dilate) to let more light in and also make it smaller to let less light in.
• Through a process called accommodation, light that enters the pupil is focused by the lens; the lens is curved and flexible in order to focus the light.
• As the light passes through the lens, the image is flipped upside down and inverted.
• The focused inverted image projects on the retina, which is like a screen on the back of your eye.

Step Three: Transduction

• Transduction refers to the translation of incoming stimuli into neural signals.
• In vision, transduction occurs when light activates the neurons in the retina.
• Rods outnumber cones (the ratio is approximately twenty to one) and are distributed throughout the retina.
• Cones are concentrated toward the center of the retina.
• At the very center of the retina is an indentation called the fovea that contains the highest concentration of cones.
• If enough rods and cones fire in an area of the retina, they activate the next layer of bipolar cells.
• If enough bipolar cells fire, the next layer of cells, ganglion cells, is activated.
• The axons of the ganglion cells make up the optic nerve that sends these impulses to a specific region in the thalamus called the lateral geniculate nucleus (LGN).
• The spot where the optic nerve leaves the retina has no rods or cones, so it is referred to as the blind spot.
• The spot where the nerves cross each other is called the optic chiasm.

Step Four: In the Brain

• Some researchers say it is at this point that sensation ends and perception begins.
• Perception researchers David Hubel (1926–2013) and Torsten Wiesel (1924–present) discovered that groups of neurons in the visual cortex respond to different types of visual images.

Theories of Color Vision

Trichromatic Theory

• The oldest and simplest theory is trichromatic theory (also called the Young-Helmholtz Trichromatic [three color] theory).
• This theory hypothesizes that we have three types of cones in the retina: cones that detect the different colors blue, red, and green (the primary colors of light).
• This theory has some research support and makes sense intuitively, but it cannot explain afterimages and color blindness.

Opponent-Process Theory

• The opponent-process theory states that the sensory receptors arranged in the retina come in pairs: red/green pairs, yellow/blue pairs, and black/white pairs.
• If one sensor is stimulated, its pair is inhibited from firing.
• This theory explains color afterimages well.

Hearing

• Sound waves, not electromagnetic waves, strengthen our hearing.
• Our ears pick up sound waves from airborne vibrations.
• The brain receives neural messages from these vibrations.
• Amplitude is the height of the wave and determines the loudness of the sound, which is measured in decibels.
• Frequency refers to the length of the waves and determines pitch, measured in megahertz.
• The waves travel down the ear canal (also called the auditory canal) until they reach the eardrum or tympanic membrane.
• The eardrum connects with the hammer (or malleus), which is connected to the anvil (or incus), which connects to the stirrup (or stapes).
• The vibration of the eardrum is transmitted by these three bones to the oval window, a membrane very similar to the eardrum.
• The oval window membrane is attached to the cochlea, a structure shaped like a snail’s shell filled with fluid.
• The floor of the cochlea is the basilar membrane.
  • It is lined with hair cells connected to the organ of Corti, which are neurons activated by movement of the hair cells.
• Place Theory - Place theory holds that the hair cells in the cochlea respond to different frequencies of sound based on where they are located in the cochlea.

Frequency Theory

• Research demonstrates that place theory accurately describes how hair cells sense the upper range of pitches but not the lower tones.
• Lower tones are sensed by the rate at which the cells fire.
• We sense pitch because the hair cells fire at different rates (frequencies) in the cochlea.

Deafness

• Conduction deafness occurs when something goes wrong with the system of conducting the sound to the cochlea (in the ear canal, eardrum, hammer/anvil/stirrup, or oval window).
• Nerve (or sensorineural) deafness occurs when the hair cells in the cochlea are damaged, usually by loud noise.

Touch

• If touch or temperature receptors are stimulated sharply, a different kind of nerve ending called pain receptors will also fire.
• Pain is a useful response because it warns us of potential dangers.

Gate-control theory

• Helps explain how we experience pain the way we do.
• Gate-control theory explains that some pain messages have a higher priority than others.

Chemical Senses

Taste (or Gustation)

• Taste buds are located on papillae, which are the bumps you can see on your tongue.
• Taste buds are located all over the tongue and some parts of the inside of the cheeks and roof of the mouth.
• Humans sense five different types of tastes: sweet, salty, sour, bitter, and umami (savory or meaty taste).
• Some taste buds respond more intensely to a specific taste and more weakly to others.

Smell (or Olfaction)

• Our sense of smell also depends on chemicals emitted by substances.
• Some researchers estimate that as many as 100 different types of smell receptors may exist.
  • These receptor cells are linked to the olfactory bulb, , which gathers the messages from the olfactory receptor cells and sends this information to the brain.

Body Position Senses

Vestibular Sense

• Our vestibular sense tells us about how our body is oriented in space.
• Three semicircular canals in the inner ear give the brain feedback about body orientation.

Kinesthetic Sense

• While our vestibular sense keeps track of the overall orientation of our body, our kinesthetic sense gives us feedback about the position and orientation of specific body parts.
• Receptors in our muscles and joints send information to our brain about our limbs.
  • This information, combined with visual feedback, lets us keep track of our body.

Perception

Thresholds

• The absolute threshold is the smallest amount of stimulus we can detect.
• The difference threshold, sometimes called just-noticeable difference, is the smallest amount of change needed in a stimulus before we detect a change.
• This threshold is computed by Weber’s law, named after psychophysicist Ernst Weber 1887).
  • It states that the change needed is proportional to the original intensity of the stimulus.

Perceptual Theories

• are theories that explain how people perceive and interpret the world around them.
• These theories focus on how people process sensory information and how they use that information to form mental representations of the world.

Signal Detection Theory

• Signal detection theory investigates the effects of the distractions and interference we experience while perceiving the world.
  • This area of research tries to predict what we will perceive among competing stimuli.
• A false positive is when we think we perceive a stimulus that is not there.
• A false negative is not perceiving a stimulus that is present.

Top-Down Processing

• When we use top-down processing, we perceive by filling in gaps in what we sense.
• Top-down processing occurs when you use your background knowledge to fill in gaps in what you perceive.
  • Our experience creates schemata, mental representations of how we expect the world to be.
• Schemata can create a perceptual set, which is a predisposition to perceiving something in a certain way.

Bottom-Up Processing

• Bottom-up processing, also called feature analysis, is the opposite of top-down processing.
• Instead of using our experience to perceive an object, we use only the features of the object itself to build a complete perception.

Principles of Visual Perception

• One of the first perceptual decisions our mind must make is the figure-ground relationship.
• One example is the famous picture of the vase that if looked at one way is a vase but by switching the figure and the ground can be perceived as two faces

Gestalt Rules

• At the beginning of the twentieth century, a group of researchers called the Gestalt psychologists described the principles that govern how we perceive groups of objects.
  • The Gestalt psychologists pointed out that we normally perceive images as groups, not as isolated elements.
• Proximity - Objects that are close together are more likely to be perceived as belonging in the same group.
• Similarity - Objects that are similar in appearance are more likely to be perceived as belonging in the same group.
• Continuity - Objects that are arranged in a continuous line or curve (such as a trail or a geometric figure) are more likely to be perceived as belonging in the same group
• Closure - Similar to top-down processing.
  • Objects that make up a recognizable image are more likely to be perceived as belonging in the same group even if the image contains gaps that the mind needs to fill in.

Constancy

• Our ability to maintain a constant perception of an object despite these changes is called constancy.
• Size constancy - We estimate size based on distance, but closer objects produce larger retinal images.
  • If we know the typical size of an object, we know that it does not grow or shrink as it moves closer or farther away.
• Shape constancy - Objects seen from different angles appear different on our retinas, but their shape is constant.
  • Due to shape constancy, we know the top of a coffee mug is circular even though it appears elliptical on our retinas.
  • Again, this depends on our familiarity with the object's usual shape.
• Brightness constancy - Despite changing light reflection, we see objects as a constant color.
  • As daylight fades, we still see a brick wall as brick red.

Perceived Motion

• Our brains are able to detect how fast images move across our retinas and to take into account our own movement.
• A common example of this is the stroboscopic effect, used in movies or flip books.
  • Images in a series of still pictures presented at a certain speed will appear to be moving.
• Phi phenomenon - A series of lightbulbs turned on and off at a particular rate will appear to be one moving light.
• Autokinetic effect - If a spot of light is projected steadily onto the same place on a wall of an otherwise dark room and people are asked to stare at it, they will report seeing it move.

Depth Cues

• One of the most important and frequently investigated parts of visual perception is depth.
  • Without depth perception, we would perceive the world as a two-dimensional flat surface, unable to differentiate between what is near and what is far.
• Researcher Eleanor Gibson used the visual cliff experiment to determine when human infants can perceive depth.
• Researchers divide the cues that we use to perceive depth into two categories:
  • Monocular cues (depth cues that do not depend on having two eyes)
  • Binocular cues (cues that depend on having two eyes).

Monocular Cues

• Artists use these cues to imply depth in their drawings.
  • One of the most common cues is linear perspective.
• Relative size cue in monocular cues is a cue used by the human visual system to determine the relative size of objects in a scene.
  • It is based on the fact that objects that are further away appear smaller than objects that are closer.
• Interposition cue in monocular cues is a type of depth perception that relies on the relative position of objects in the field of view.
  • It is based on the idea that if one object is blocking the view of another object, then the object that is blocked must be further away.
• Texture gradient- we know that we can see details in texture close to us but not far away.
• Shadowing - By shading part of your picture, you can imply where the light source is and thus imply depth and position of objects.

Binocular Cues

• Binocular cues are visual cues that are used by the brain to determine depth and distance.
  • They are based on the fact that the two eyes are slightly separated, so they see the same object from slightly different angles.
  • This allows the brain to calculate the distance and depth of the object.
• Binocular disparity is the difference in the images seen by each eye.
  • This difference is used by the brain to calculate depth and distance.
  • Binocular disparity is an important part of stereopsis, which is the ability to perceive depth and distance.
• Convergence in binocular cues is the process of both eyes turning inward to focus on an object that is close to the viewer.
  • This process helps the viewer to accurately judge the distance of the object.
• Extrasensory Perception - Psychologists are skeptical of ESP claims primarily because our senses are well understood, and researchers do not find reliable evidence that we can perceive sensations other than through our sight, smell, hearing, taste, touch, and vestibular/balance systems.