Sensation and Perception: Chapter 1

Introduction to perception

The first Perceptron, created by psychologist Frank Rosenblatt (1958)

room-sized five-ton computer that could teach itself to distinguish between basic images

many now consider Rosenblatt’s work to be a key precursor to

modern artificial intelligence

Why did early computer scientists think they would be able to create a computer capable of human-like perception within a decade or so, and we still aren’t there yet?

perception!

perception

the experiences that result from stimulation of the senses

• conscious sensory experience

he mechanisms responsible for perception are

extremely complex.

the detectors

located in the eyes, ears, skin, tongue, nose, and mouth

the “computer”

the brain

Medical applications that depend on an understanding of perception include

devices to restore perception to people who have lost vision or hearing and treatments for pain

Other applications of perception

autonomous vehicles that can find their way through unfamiliar environments, face recognition systems that can identify people as they pass through airport security, speech recognition systems that can understand what someone is saying, and highway signs that are visible to drivers under a variety of conditions.

Studying perception can help you become

more aware of the nature of your own perceptual experiences.

perception is something you experience

constantly

There are things out there that you want to see, hear, taste, smell, and feel. But the only way to achieve this is by activating

sensory receptors

sensory receptors

designed to respond to light energy, sound energy, chemical stimuli, and pressure on the skin

whatever you are feeling depends on the

activation of these receptors.

perception depends on

the properties of the sensory receptors

sensation

often identified as involving simple “elementary” processes that occur right at the beginning of a sensory system, such as when light reaches the eye, sound waves enter the ear, or your food touches your tongue

perception is identified with complex processes that involve

higher-order mechanisms such as interpretation and memory that involve activity in the brain

• example: identifying the food you’re eating and remembering the last time you had it

sensation involves detecting…

elementary properties of a stimulus

perception involves the higher brain functions involved in

interpreting events and objects

dot example: even a stimulus this simple can be

seen in more than one way

• example: one dot, a triangle, a house

• illustrates that deciding what is sensation and what is perception is not always obvious or even that useful

calling some processes sensation and others perception doesn’t add anything to our understanding of

how our sensory experiences are created, so the term perception is used almost exclusively throughout this book

Perhaps the main reason not to use the term sensation is that

the term sensation appears only rarely in modern research papers (mainly in papers on the sense of taste, which refer to taste sensations, and touch which refer to touch sensations), whereas the term perception is extremely common.

Sensation was discussed in the

arly history of perceptual psychology, and courses and textbooks followed suit by including sensation in their titles

perceptual process

A sequence of steps leading from the environment to perception of a stimulus, recognition of the stimulus, and action with regard to the stimulus.

• 7 steps

Step 1: perceptual process

stimulus in the environment

step 2

stimulus hits the receptors

step 3

receptor processes

step 4

neural processing

step 5

perception

step 6

recognition

step 7

action

information about the stimulus in the environment (the distal stimulus)

step 1

information hits the receptors, resulting in the proximal stimulus

step 2

• a representation of the stimulus on the retina

receptor processes include transduction and the shaping of perception by the properties of the receptors

step 3

neural processing involves interactions between the electrial signals traveling in networks of neurons

step 4

finally, the behavioural responses are generated (steps 5-7)

perception, recognition, and action

“neural processing” involves understanding not only how cells called neurons work, but how they

interact with each other and how they operate within different areas of the brain.

Another reason we say that our process is simplified is that steps in the perceptual process do

not always unfold in a one-follows-the-other order.

research has shown that perception and recognition may not

always happen one after another, but could happen at the same time, or even in reverse order

there are bidirectional arrows between

perception, recognition, and action

there is also an arrow from action back to the stimulus

perceptual process as a cycle in which taking action changes the observer’s view (for example)

distal stimulus

The stimulus “out there,” in the external environment. (step 1)

• example: tree the person is observing

proximal stimulus

The stimulus on the receptors. In vision, this would be the image on the retina. (step 2)

• example: the representation of the tree on the receptors

the principle of transformation

stimuli and responses created by stimuli are transformed, or changed, between the distal stimulus and perception.

• one of the central principles of perception

• example: the light and pressure waves that stimulate the receptors

tree example: the first transformation

when light hits the tree and is then reflected from the tree to the person’s eyes.

• the nature of the reflected light depends on properties of the light energy hitting the tree

principle of representation

everything a person perceives is based not on direct contact with stimuli but on representations of stimuli that are formed on the receptors and the resulting activity in the person’s nervous system.

• another principle of perception

the distinction between the distal stimulus (step 1) and the proximal stimulus (step 2), illustrates both

transformation and representation.

Sensory receptors are

cells specialized to respond to environmental energy, with each sensory system’s receptors specialized to respond to a specific type of energy

• examples: visual receptors → light, auditory receptors → pressure changes in the air

When the sensory receptors receive the information from the environment, they do two things:

1. They transform environmental energy into electrical energy

2. they shape perception by the way they respond to different properties of the stimuli

The transformation of environmental energy (such as light, sound, or thermal energy) to electrical energy is called

Transduction

Transduction

In the senses, the transformation of environmental energy into electrical energy. For example, the retinal receptors transduce light energy into electrical energy

purpose of transduction

• to allow distal information to be transformed into a form that can be understood by your brain

• transduction by the sensory receptors is crucial for perception

neural processing: signals travel through a vast interconnected network of neurons that

1. transmit signals from the receptors to the brain and then within the brain; and

2. change (or process) these signals as they are transmitted

The changes in these signals that occur as they are transmitted through this maze of neurons is called

neural processing

neural processing.

Operations that transform electrical signals within a network of neurons or that transform the response of individual neurons

there are commonalities in neural processing between

the senses

the electrical signals created through transduction are often sent to a sense’s

primary receiving area in the cerebral cortex of the brain

primary receiving area

Area of the cerebral cortex that first receives most of the signals initiated by a sense’s receptors. For example, the occipital cortex is the site of the primary receiving area for vision, and the temporal lobe is the site of the primary receiving area for hearing

The cerebral cortex

The 2-mm-thick layer that covers the surface of the brain and contains the machinery for creating perception, as well as for other functions, such as language, memory, and thinking.

The primary receiving area for vision occupies most of the

occipital lobe

the area for hearing is located in part of the

temporal lobe

the area for the skin senses—touch, temperature, and pain—is located in an area in the

parietal lobe

frontal lobe

receives signals from all of the senses, and it plays an important role in perceptions that involve the coordination of information received through two or more senses.

after all of that transformation, transduction, transmission, and processing, we reach the

behavioral responses

the conscious experience of perception when electrical signals have been transformed to such

is step 5

tree example: perception

conscious awareness of the tree

tree: recognition

placing the object into a category, “tree”, that gives it meaning

The behavioral responses of the perceptual process:

perception, recognition, action

the case of Dr. P.

• began having trouble recognizing his students visually

• misperceiving common objects

• the man who mistook his wife for a hat?

• but he could see well

what was Dr. P diagnosed with

visual object agnosia

• was caused by a brain tumor

• perceived the parts of objects but couldn’t identify the whole object

visual object agnosia

an inability to recognize objects

The final behavioral response is action (Step 7), which involves

motor activities in response to the stimulus.

example of step 7

after having perceived and recognized the tree, the person might decide to walk toward the tree, touch the tree, have a picnic under it, or climb it.

Some researchers see action as an important outcome of the perceptual process because of its importance for

survival

David Milner and Melvyn Goodale (1995)

propose that early in the evolution of animals, the major goal of visual processing was not to create a conscious perception or “picture” of the environment but to help the animal control navigation, catch prey, avoid obstacles, and detect predators—all crucial functions for the animal’s survival.

one more factor: knowledge.

any information that the perceiver brings to a situation, such as prior experience or expectations.

• top-down processing

• can affect steps in the perceptual process

rat–man demonstration

The demonstration in which presentation of a “ratlike” or “manlike” picture influences an observer’s perception of a second picture, which can be interpreted either as a rat or as a man. This demonstration illustrates an effect of top-down processing on perception.

An example of how knowledge acquired years ago can influence the perceptual process is your ability to

categorize—to place objects into categories

Bottom-up processing

Processing that is based on the information on the receptors. Also called data-based processing.

top-down processing

Processing that starts with the analysis of high-level information, such as the knowledge a person brings to a situation. Also called knowledge-based processing

whether top-down processing is always involved in perception?

it is “very often” involved.

• There are some situations, typically involving very simple stimuli, in which top-down processing may not be involved. (flash of light)

as stimuli become more complex, the role of top-down processing

increases

3 major components of the perceptual process

• stimulus

• physiology

• behaviour

stimulus component

distal and proximal; steps 1-2

physiology component

receptors and neural processing; steps 3-4

behaviour component

perception, recognition, action; steps 5-7

three relationships that are usually measured to study the perceptual process are

(A) the stimulus–behavior relationship

(B) the stimulus–physiology relationship

(C) the physiology–behavior relationship.

oblique effect

Enhanced sensitivity to vertically and horizontally oriented visual stimuli compared to obliquely oriented (slanted) stimuli.

• This effect has been demonstrated by measuring both perception and neural responding.

The Stimulus–Behavior Relationship (A)

The relationship between stimuli and behavioral responses, where behavioral responses can be perception, recognition, or action.

One way to study the stimulus–behavior relationship is using an approach called

psychophysics

psychophysics

measures the relationships between the physical (the stimulus) and the psychological (the behavioral response)

Grating acuity

the smallest width of lines that participants can detect

The oblique effect has been demonstrated by

presenting black and white striped stimuli called gratings, and measuring Grating acuity,

One way to measure grating acuity is to

ask participants to indicate the grating’s orientation and testing with thinner and thinner lines

• eventually the lines are so thin that they can’t be seen, and the area inside the circle looks uniform

When grating acuity is assessed at different orientations, the results show that acuity is best for gratings oriented

vertically or horizontally, rather than obliquely

The Stimulus–Physiology Relationship (B)

the relationship between stimuli (Steps 1–2) and physiological responses, like neurons firing (Steps 3–4).

how is the stimulus-physiology relationship often studied?

by measuring brain activity

• David Coppola: oblique effect with ferrets

how did David Coppola and coworkers (1998) measure the ferret’s brain activity

using a technique called optical brain imaging

David Coppola and coworkers (1998): findings

horizontal and vertical orientations caused larger brain responses/activity in visual brain areas than oblique orientations

• results similar in humans

Horizontal and vertical orientations result in better acuity (behavioral response) and more

brain activation (physiological response) than oblique orientations.