Introduction to Perception
• Humans have been able to perceive, understand, locate, describe, identify, and be
consciously aware, a feat not yet accomplished by the world’s most powerful computers.
• Our goal is to understand the human model starting with the detectors, and then the
computer, or brain.
• Perception is not something that ‘just happens,’it takes many parts that work together
cohesively to interpret and react to the environment.
Why Read This Book?
• Studying perception can help in a medical sense, it can aid in restoring senses to those
who have lost them. This book is a stepping stone towards these sorts of goals.
• Studying perception can help you become more aware of the nature of your own
• Everything we see, hear, taste, feel, or smell is created by the mechanisms of our senses.
• Our receptors allow us to be able to receive information about the world, without them,
we would feel nothing.
• One theme of this book, “perception depends on the properties of the sensory receptors.”
The Perceptual Process
• Perceptual process: A sequence of steps leading from the environment to perception of a
stimulus, recognition of a stimulus, and action with regard to the stimulus.
• 7 steps in the perceptual process: 1) Environmental stimulus 2) Light is reflected and
transformed 3) Receptor processes 4) Neural processing 5) Perception 6) Recognition 7)
Action (3-7 are a bi-directional pathway).
• At times, these steps can co-occur or happen in reverse direction (recognition before
perception). When perception and recognition lead to action, that action can change how
we perceive or recognize, therefore the arrows are bi-directional.
Stimuli (Steps 1 and 2)
• Environmental stimulus: The stimulus “out there,” in the external environment.
• Principle of transformation: A principle of perception of stimuli and responses created by
stimuli are transformed, or changed, between the environmental stimulus and perception.
• Information from an object is carried by light, which gets reflected from the tree, travels
through the atmosphere, and focuses on the eye’s optical system. Each of these steps
involves light being transformed in one way or another.
• Eye’s optical system involves the cornea at the front of the eye and the lens directly
behind it. Light passes through these and lands on the receptors located on the retina.
• Principle of representation: A principle of perception that everything a person perceives
is based not on direct contact with the stimuli but on representations of stimuli on the
receptors and in the person’s nervous system.
• Step 1 is the environmental stimulus; step 2 is the stimulus on the receptors.
Receptor Processes/Transduction (Step 3) • Sensory receptors: Cells specialized to respond to environmental energy, with each
sensory system’s receptors specialized to respond to a specific energy type.
• When the visual receptors at the back of the eye receive light, they do one of 2 things. 1)
They transform environmental energy into electrical energy and 2) they shape perception
by the way they respond to stimuli.
• Rod and cone receptors lining the back of the eye transform light energy into electrical
energy and influence what we perceive.
• Visual pigment: A light-sensitive molecule in the rod and cone outer segments. The
reaction of this molecule to light results in the generation of an electrical response in the
• Transduction: In the senses, the transformation of environmental energy into electrical
energy. For example, the retinal receptors transduce light energy into electrical energy.
• Visual receptors can transform light into electrical energy due to having visual pigments
that react to light.
• Transduction is crucial for perception.
• The visual pigments shape perception.
Neural Processing (Step 4)
• After transduction, the electrical signals enter the vast network of neurons, first in the
retina, then out the back of the eye, and then in the brain.
• The network of neurons: 1) transmits signals from the receptors, through the retina, to the
brain, and then within the brain; and 2) change (or process) these signals as they are
• There are multiple routes for signals to take, can be amplified, reduced, travel in opposite
directions, or prevented from getting through.
• Neural processing: Operations that transform electrical signals within a network of
neurons or that transform the response of individual neurons.
• Transduction occurs for the other senses as well.
• Primary receiving area: Areas of the cerebral cortex that first receive 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.
• Occipital lobe: A lobe at the back of the cortex that is the site of the cortical receiving
area for vision.
• Temporal lobe: A lobe on the side of the cortex that is the site of the cortical receiving
area for hearing and the termination point for the ventral, or what, stream of visual
processing. A number of areas in the temporal lobe, such as the fusiform face area and
the extrastriate area, serve functions related to perceiving and recognizing objects.
• Parietal lobe: A lobe at the top of the cortex that is the site of the cortical receiving area
for touch and is the termination point of the dorsal (where and how) stream of visual
• Frontal lobe: Receiving signals from all of the senses, the frontal lobe plays an important
role in perceptions that involve the coordination of information received through two or
more senses. It also serves functions such as language, thought, memory, and motor
functioning. • Electrical signals arrive in the primary receiving area (different for each sense) of the
cerebral cortex. Vision, the primary receiving area is the occipital lobe; hearing –
temporal lobe; skin senses like touch, pain, temperature – parietal lobe; and the frontal
lobe receives signals from all of the senses. It also plays an important role in perceptions
that involve the coordination of information received through 2(+) senses.
• Many transformations occur between the visual representation and the electrical signals
reaching the brain. Though they are different signals, they still represent the same
Behavioural Responses (Steps 5-7)
• Important step because the electrical signals are transformed into conscious experience.
• Perception: Conscious sensory experience.
• Recognition: The ability to place an object in a category that gives it meaning – for
example, recognizing a particular red object as a tomato.
• Perception would be conscious awareness of an object; recognition would be placing it in
the category of ‘tree.’
• Dr. P, a musician and music teacher, began to stop recognizing people and objects. He
could determine students by the sounds of their voices, but not by seeing them.
• Visual form agnosia: The inability to recognize objects.
• Dr. P was suffering from visual form agnosia, or an inability to recognize objects, caused
by a brain tumour. He could perceive an object and recognize the parts of it, but was
unable to perceptually assemble the parts in a way that would enable him to recognize the
object as a whole.
• Action: Motor activities such as moving the head or eyes and locomoting through the
environment. Action is one of the major outcomes of the perceptual process.
• Action can also be considered a lack of action. Choosing to stay in place is still an action.
• Early proposal was the purpose of visual processing was not to create a conscious
perception, but to create action that would enable survival.
• Perception is a continuously changing process. The overall process is dynamic and
• Knowledge: Any information that the perceiver brings to a situation.
• Rat-man demonstration: The demonstration in which presentation of a “ratlike” or
“manlike” picture influence an observer’s perception of a second picture, which can be
interpreted as a rat or as a man. This demonstration illustrates an effect of top-down
processing on perception.
• Previous knowledge influences how you interpret new stimuli.
• Bottom-up processing (AKA data-based processing): Processing that is based on the
information on the receptors. Processing that is based on incoming data as opposed to
top-down (knowledge-based) processing, which is based on prior knowledge.
• Top-down processing (AKA knowledge-based processing): Processing that starts with
the analysis of high-level information such as the knowledge a person brings to the
• Example:Adoctor gives you a prescription. You bring it to the pharmacist who needs to
decipher the unreadable scribble. Seeing the scribble is the image on the receptors, interpreting the scribble using the pharmacist’s knowledge of drugs or perhaps the
doctor’s writing allows the pharmacists to use her prior knowledge in the situation.
• In most cases of perception, though not all, top-down processing is involved.Acase