COG-PSY, CH 2

Sensation and Perception are used to describe different stages in the
process by which we acquire information from the world.
1. In sensation, raw physical energy is absorbed by our eyes, ears, and
other sensory receptors.
2. Through the process of transduction, raw energy from sense receptors
is converted into neural signals that are sent to the brain.
3. In perception, neural signals are selected, organized, and interpreted.
 Psychophysics: the study of the relationship
between physical stimuli and subjective sensations.

The Process of Sensation-Perception
◊ Absolute Thresholds: Is the smallest amount of
stimulation that can be detected.
– Absolute thresholds are different for each person, it is
defined as the point at which a stimulus can be detected
50% of the time.
What is the minimum amount of light that can be seen, the
weakest vibration that can be heard, or the faintest odor
than can be smelled!

Vision: a lit candle 30 miles away on a dark clear night.
 Hearing: the tick of a watch 20 feet away in a quite room.
 Smell: 1 drop of perfume dispersed throughout a 3 room apartment
 Taste: 1 teaspoon of sugar in two gallons of water.
 Touch: the wing of fly falling on your cheek from a height of 3
inches.

The Process of Sensation-Perception
◊ Difference Thresholds: sensory capacities are not
only measured by our ability to detect low levels of stimulation like in
absolute thresholds, but also by the extent to which we can detect
subtle differences from another comparative stimulus.
◊ Example: we can ask subjects to compare the
brightness of two light bulbs; the loudness of two
tones; the weight of two blocks, and so on.

The Process of Sensation-Perception
Just Noticeable Difference (JND): allows us to compare the sensitivities
of different sensory modalities.
The smaller the JND, the more sensitive the sense modality!
Vision is the most sensitive sensory modality followed by movement!

The Process of Sensation-Perception
 Psychophysics: the study of the
relationship between physical stimuli
and subjective sensations.
 Fechner developed the signal
detection theory in order to examine
these subjective reports to a
sensation.
 Detecting a stimulus is jointly
determined by the signal strength
and subjects response criterion
(his or her willingness to say yes
rather than no).

The Process of Sensation-Perception
• Hit: saying yes when the stimulus is present.
• Miss: No means Yes-the stimulus was present.
• Correct Rejection: No means No!
• False alarm: saying yes when the stimulus is not
present which is a response bias.
 This method will allow the psychophysicist to determine
detection performance from response bias by looking at
the percentage of each response.

How It Works: The Case of Visual Perception
Top-Down and Bottom-Up Processing:
1. Bottom-Up: are driven by sensory information from the
physical world and more objective.
2. Top-Down: actively seek and extract sensory
information and are driven by our knowledge,
beliefs, expectations, and goals.
Top-down is more cognitive than bottom-up, but can also
be more misleading--errors in perception!

 Bottom Up Processes:
 The Stimulus for Vision?
 Humans see light within a narrow band of electromagnetic
radiation--Light.
 We see wavelengths of light between 380 to 760 nanometers
(a nm is a billionth of a meter).

1- Cornea: bends light
to sharply focus it
within the eye.
2- Iris and Pupil:
regulates and
focuses light onto
the lens.
3- Lens: Focuses
images on the
Retina
4- Retina: contains
photoreceptors.

Human Photoreceptors: The human retina has a
mixture of rods and cones.
 Cone-Mediated Vision:
 6 million cones in the retina, specifically in
the fovea (center).
 Predominates in good lighting.
• Provides high–acuity (fine-detailed)
• Colored perceptions of the world.
 In dim light, there is not enough light to reliably
excite the cones.

Anatomy of the Visual System
 Photoreceptors
 Rod-Mediated Vision:
• 120 million rods in the retina but they are
located outside of the fovea.
• Do not detect differences in color and
provide poor visual acuity.
• Sensitive to light of low intensity.

Color Vision
 Photoreceptors: Trichromatic Coding
 Peak sensitivities of the three cones:
 Blue cone: Short-wavelength
 Blue hue ( 420 nm )
 Green cone: Medium-wavelength
 Green hue( 530 nm )
 Red Cone: Long-wavelength
 Red hue( 560 nm )

 Visual Transduction: The conversion of Light to
Neural Signals
• Visual Transduction:
• Is the conversion of light to neural signals by
visual receptors.
• Rods and Cones in the Retina convert light into
an electrical/neural signal that goes through the
visual pathway for sensation/perception.

Anatomy of the Visual System
 Connection between Eye and Brain
 The optic nerve (made by retinal ganglion cells)
leave the retina to form an X shape at the optic
chiasm before reaching the LGN of thalamus.

Anatomy of the Visual System
 The DLGN of Thalamus: There are two layers/groups of
cells in each DLGN.
 Parvocellular Layers (3, 4, 5, 6): are composed of
neurons with small cell bodies.
 Magnocellular Layers (1 & 2): are composed of neurons
with large cell bodies.

Anatomy of the Visual System
 Parvocellular Neurons:
Receptive to Color
Patterns & Details of Objects
 Cones provide the majority of input to this layer.
 Magnocellular Neurons:
 Responsive to Movement.
 Responsive to Dim Light.
 Rods provide the majority of input to this layer.

Anatomy of the Visual System
The magnocellular and parvocellular from
LGN project to the primary visual cortex.

 Anatomy of the Visual System
Optic nerve from LGN of Thalamus then goes to the primary
visual cortex in the brain.
The primary visual cortex is where seeing takes place!
** Even when we dream, this area is active—visual perception
in the absence of environmental sensation!

Analysis of Visual Information:
Role of the Striate Cortex
 David Hubel and Torsten Wiesel:
— Feature detectors—neurons that are sensitive
only to certain aspects of a visual image.
 These cells are important for recognition of
patterns into objects, but are bottom up cells.

The Duality of Visual Processing
Beyond the primary visual cortex, two main pathways
can be identified:
(1) A dorsal Stream that leads to the parietal lobe region.
They call this the “Where pathway of Vision”
– Important in processing information about where items are
located in space and how they might be acted on, guiding
movements such as grasping.
–Attention toward visual objects are guided here!

The Duality of Visual Processing
Beyond the primary visual cortex, two main pathways
can be identified:
(2) A ventral pathway that leads to the temporal lobe region.
They call this the “What pathway of Vision”
This pathway processes information that leads to the recognition
and identification of objects.
FYI--this pathway very active in dreaming as temporal lobes hold
the amygdala/hippocampus!

Learning to Perceive
Sensation-Perception Biologically Hard Wired or
Learned?
At birth, parts of the eye and visual cortex are not fully developed.
They can not detect subtle differences in light, shading, or color.
Despite these limitations in the newborns visual capabilities, they
develop quickly and have preferences for certain kinds of
stimulation.
Frantz (1961):
Recorded the amount of time that 2-5 day old infants spent gazing
at 6 disks presented with different images:
Complex Stimuli: human face, bulls eye, news print.
Simple Stimuli: 3 solid colored disks: red, white, and yellow.

Learning to See
Frantz (1961): Results
1-The infants preferred to look at the complex patterns to simple
solids.
2- New born favorite pattern was the human face.
This may suggest that newborns come equipped or have an innate
preference for social stimuli that is hard-wired in the visual-
perceptual system.
Johnson (1991): tested whether newborns are innately social or
prefer more complex patterns irrespective of design.
The premise was that human face is more complex than a bulls
eye.
Newborns may like staring at complex patterns rather than the
human face. Giving something more complex than human face
and let’s see!!

Learning to See
Johnson (1991):
In this study, newborns were presented with 3 complex patterns:
• Properly featured face
• Scrambled face that is considered to be a more complex pattern
• Bland featureless face that is not complex at all.
The researchers recorded the extent to which infants rotated their heads
and eyes to follow visual stimuli.
Results: Both head and eye movements were greatest for the properly
featured face then for the complex patterned scrambled face.
Conclusion: humans are born with a special orientation toward the face
and are innately sociable. This innate preference can be seen as an
adaptive quality because it will facilitate social learning and imitation.

Evidence that Sensation-Perception
is Bottom up Process!
Gestalt Psychology was the first school of
thought that examined how perceptions
emerge and are organized from
sensations.
They argued that sensation-perception was
innate since grouping principles are
universal!

Grouping Principles
Gestalt Psychology:
Max Wertheimer, the founder of gestalt psychology in 1912,
argued that humans have an inborn tendency to construct
meaningful perceptions from fragments of sensory input.
He called this notion perceptual organization.
The first gestalt principle of perceptual organization is that
people automatically focus on some objects in the perceptual
field to the exclusion of others.
What we focus on is called the figure and what fades is called
the ground.

Figure-Ground Effect:

Gestalt Laws of Grouping: Another principle of perceptual organization is that we tend to group collections of shapes, sizes, colors, and other eatures into perceptual wholes.

Grouping rules are proximity, similarity, continuity, closure, and common fate

Since infants group stimulus objects in predicted ways, these tendencies are inborn

Grouping Principles
Gestalt Laws of Grouping:
• Proximity: The closer objects are to one another, the more
likely they are to be perceived as a unit.

Spatial or temporal proximity of elements may induce the
mind to perceive a collective or totality.

Gestalt Laws of
Grouping:
• Similarity: objects
that are similar in
shape, size, color, or
any other feature tend
to be grouped
together.

Continuity:
People perceive
the contours of
straight and
curved lines as
continuous
flowing patterns.

Closure: When there are gaps in a pattern that resembles a familiar
form, people mentally close the gaps and perceive the object as a whole.
 This tendency enables us to recognize imperfect representations in hand
drawings, written material and so on.

Gestalt Laws of Grouping:
 The gestalt school of thought laid an important foundation for perceptual
psychology to develop.
 They describe how people transform raw input into meaningful displays.
 They are applied to static objects and not at radical changes in sensory input.
 Modern perceptual psychology looks at what happens to our perception when
we move about and not remain static within the environment.
 perceptual constancies allow perceptions to remain stable despite radical
changes in sensory input

Perceptual constancies:
Size Constancy: Is the tendency to view objects as constant in size despite
changes in the size of its image on the retina.
 An example is when a person walks away and grows smaller in size with
distance.
 Despite the perception that the person is changing in height, we know that
this is not the case because of our experiences—bottom up or top down?
 As objects move around in space, we perceive the change in distance and
adjust our size perceptions accordingly.

Perceptual constancies:
Shape Constancy: Is the tendency to see an object as retaining its
form despite changes in orientation.
For example, take a quarter and if the head side is facing you it will
seem circular.
Turn it 45 degrees and it will appear elliptical.
Turn it another 45 degrees and will appear like a straight line on the
retina.

Models of Recognition
Visual Recognition involves the match between sensory
information and the corresponding representation stored in
long-term memory.
The sensory-perceptual representation is built in the visual
pathway, but assigned meaning and categorized based on
prior experience which is pulled from LTM.
The following are models of this process in LTM:
 Template-Matching Models
 Feature-Matching Models
 Recognition-by-Components Model

The template-matching method: involves a direct match
between the sensory experience and the literal copy (or template)
of that experience which is stored in LTM.
The mapping process is made on the basis of perfect overlap
between the sensory pattern and the template.
This is a simple Lock-and-Key type of hypothesis. The match
continues until a template is found that fits the sensory
experience!
 This model can not account for the accuracy and flexibility of
pattern recognition.

Feature-matching models search for simple but characteristic
features of an object; their presence signals a match.
This model is more flexible and general relative to template models.
It can recognize objects based on relevant features such as vertical
lines, curves, or diagonals.
Features such as line segments and curves could serve as a general-
purpose building block for recognizing other, more complex visual
patterns such as chairs, jackets, cars or to recognize the many
variations found within one object.
With these basic features innately catalogued, you can start
assembling larger units.
Separate brain mechanisms put the features together, assembling
them into complete objects/larger units.

Recognition by Components Model (RBC):
• Geons (short for geometric ions) serve as the basic
building blocks of all object recognition.
• Geons are simple shapes such as cylinders, cones, and
blocks.
• According to Biederman, there are 3-dozen geons and
are in essence the alphabet from which all objects are
constructed.
• The 3-dozen geons describe every object in the world, as
26 letters are all that are needed to produce all words in
the English language.

Biederman’s Geons (geometrical ions)
 Geons can be combined in various ways to create all the
objects we perceive in the world.
 For example, a bucket contains Geon 5 (top connected)
to Geon 3.

Biederman’s Geons (geometrical ions)
 Recognition by Components:
• Physiological evidence in primates supports the notion
that our brains support geons in object recognition.
• Kayaert, Biederman, and Vogels (2003) found that
neurons in the temportal cortex of monkeys responded
selectively to simple geometric shapes.
• Some neurons responded best to cylinders, others to
cones, and still others best to boxes

Autism and Face Recognition
―The face processing difficulty in Autism extends beyond
simple face recognition, but also affecting perceptual
discrimination of faces too!
―Autistic individuals perform more poorly on same/different
judgment tasks than controls
n the different condition, the 2 faces could each be a different gender or they
could share the same gender but be 2 different individuals.

Autism and Face Recognition
―Blaire et al.(2002): compared visual memory of faces and
objects in autistic and controls.
―The individuals with autism presented selective impairments
in face recognition in comparison to age-matched controls.
―In contrast, autistic individuals were selectively superior
relative to the comparison group on the recognition memory for
objects as buildings and leaves.
―Findings suggest that autistic individuals do not have deficits
with visual memory in general, but is specific to face/person
processing.
―Their different perceptual system may explain why they have
trouble with social communication skills!

Autism and Eye Gaze-Tracking
Eye Tracking Project in Autism : Jones et al. (2008): study
compared eye tracking in Autistic toddlers (2 years old) with
age matched controls
Findings:
― Age-matched controls zero in on the eyes, and other facial features
like the mouth which convey subtle social and emotional cues.
– Individuals with autism, even as 15-month-old babies, completely
avoid eye gaze, and only 38% spent time gazing at mouth and other
facial features!
– Sensory-perceptual deficits are tied to social deficits which in turn
may play a causative role in the emergence of other characteristics
manifest in autism, such as language delay!

Eye Tracking and Brain imaging: observed relationship between
gaze patterns and brain activation in autism!
Dalton et al. (2005) found not only diminished eye region
fixation but reduced neural activity in the fusiform gyrus in
subjects with autism.
The Fusiform gyrus extends from the temporal to occipital lobe
regions of the cortex. Generally involved with the following
behaviors:
1. Processing of color information
2. Face and body recognition
3. Visual word recognition
4. Perception of emotional facial stimuli
Prosopagnosia is a disorder commonly found in patients with
brain injury to the fusiform area where they suffer from face
blindness. No deficits in object recognition or decision making!

A Brain That Cannot Recognize
Recognition is the process of matching representations of
organized sensory input to stored representations in memory.
There are people who have no sensory deficit at all who
nonetheless cannot readily recognize the objects around them.
This condition, which is called agnosia (literally, “without
knowledge”), results from damage to the brain, not to the sensory
organs.
When sight is unimpaired and yet recognition fails, the deficit is
known as visual agnosia.
Most cases of visual agnosia are brought about through cerebral
vascular accidents (Zoltan, 1996).

A Brain That Cannot Recognize
Visual Agnosia: Patient-J had a stroke that damaged parts of the
occipital and left temporal lobe:
•He was able to make out forms and objects so sensory input intact.
•He did not know the names or purposes of objects.
•Had difficulty recognizing his own wife.
• He could describe objects as they appear indicating no loss of
feature detection or bottom up processing.
•He was able to describe objects through touch--indicating language
ability intact but selective impairment in visual recognition.
•There are several models that describe visual recognition.