Sensation and Perception Flashcards
What is sensation?
The passive process of bringing information from the outside world into the body and to the brain.
The process is passive in the sense that we do not have to be consciously engaging in a “sensing” process.
What is perception?
The active process of selecting, organizing, and interpreting the information brought to the brain by the senses.
How does sensation occur?
Sensation occurs like this:-
a) Sensory organs absorb energy from a physical stimulus in the environment.
b) Sensory receptors convert this energy into neural impulses and send them to the brain.
c) This process is referred to as transduction.
What do we mean by transduction?
-Communication between the brain & the
rest of the body (& between different
regions of the brain) occurs via neuron.
-All senses involve something called
receptor cells. Their job is to transduce
(transform or even “translate”) physical
stimulation/physical energy from the
environment into electrochemical
messages that can be understood by the
brain.
Perception follows transduction.
a) the brain organizes the information and translates it into something meaningful.
b) But what does “meaningful” mean?
How do we know what information is important and should be focused on? = Sensation perception process.
The Sensation-Perception
Process
-The process of seeing an object and recognizing it as a car, house or whatever
The process of seeing an object and recognizing it as a flower, for example, would involve the following steps:
- Energy signals in the environment reach the specialized receptor cells in the eyes
- These specialized receptor cells turn the energy signal into an electrochemical impulse as part of a process called transduction.
- The impulse is then sent to the relevant brain region(s), and sensation occurs
- The brain makes meaning of the message, and perception occurs
- While sensation involves picking up the bits of signals from the environment, perception involves making meaning of this information.
The energy signals to which the various senses respond.
Selective attention and Perpetual expectancy
1) Selective Attention - the process of discriminating between what is important & is irrelevant and selective attention is influenced by motivation.
2) Perceptual Expectancy - how we perceive the world is a function of our past experiences, culture, and biological makeup. When we look at a highway, we expect to see cars, trucks, etc, NOT airplanes. But someone from a different country with different experiences and history may not have any idea what to expect and thus be surprised when they see cars go driving by.
What is psychophysics?
The study of how physical stimuli are translated into psychological experience.
-Sternberg (2004) explains psychophysics as the study of the physical energy stimulation of the sensory organs which resulted in meaningful psychological experience
In order to measure these events, psychologists use THRESHOLDS.
Thresholds
- The level of energy that a stimulus must have in order for an organism to perceive it.
- The Absolute threshold is the minimum amount of energy required for an organism to detect a stimulus
- Weber’s law, the First Law of Psychophysics (Holt et al., 2012), states that noticing a change depends on the proportion by which the stimulus has changed
- Adaption to Stimuli: When we are constantly surrounded by a particular stimulus and start to block it out.
- Occurs at the same rate regardless of how recently we adapted to the stimuli
- This is a process over which we have little conscious control
Signal detection theory
People do not always detect a signal at the same time or in the same way, and sometimes they even get it wrong
Discriminating between stimuli:
- Difference threshold is the minimum amount of stimulus intensity change needed to produce a noticeable change.
- Just noticeable difference (JND) the level at which people will notice a difference between 2 stimuli 50% of the time, and this is the minimum level of difference required for a sense to know
the stimuli have changed or become different
Therefore, JND defines differences
Example: Difference Threshold
The greater the intensity (ex., weight) of a stimulus,
the greater the change needed to produce a
noticeable change.
-When you pick up a 5 kg weight, and then a 10
kg weight, you can feel a big difference between
the two. However, when you pick up 100 kg, and
then 105 kgs, it is much more difficult to feel the
difference.
Detection of a stimulus involves some decision making process as well as a sensory process.
Additionally, both sensory and decision-making processes are influenced by many more factors than just intensity.
a) Noise - how much outside interference exists.
b) Criterion - the level of assurance that you decide must be met before you take action. Involves higher mental processes. You set criteria based on expectations and consequences of inaccuracy.
- At a party, you order a pizza…you need to pay attention so that you will be able to detect the appropriate signal (doorbell), especially since there is a lot of noise at the party.
- But when you first order the pizza, you know it won’t be there in 2 minutes, so you don’t really pay attention for the doorbell. As the time for the pizza to arrive approaches, however, your criterion changes…you become more focused on the doorbell and less on extraneous noise
VISION
Light
- The energy signal that the human eye receives is light
- Light is a form of electromagnetic radiation, which is in the form of wavelengths.
- Humans can only detect wavelengths ranging between 350 and 750 nanometres (or billionths of a metre)
Structure of the Eye
Specialist cells in the eye pick up light in the form of wavelengths
-Before the light energy reaches these cells, it first has to travel through the eye itself
The route that light travels it goes through the following steps:
- The light hits the cornea of the eye
- Light passes through the pupil
#The iris is the colored part of the eye that surrounds the pupil. Sternberg (2004) explains that the iris is a circular band muscles that make the iris bigger or smaller
- The light passes through the lens
- The bent light that is focused onto the back of the eye hits the retina
- The retina’s specialized neurons include cells called photoreceptor cells, which change the electromagnetic energy of light into electrochemical energy (the neutral impulse), which can be relayed to the brain.
There are 2 types of photoreceptors: rods and cones, thus named because of their distinctive shape.
- Rods enable us to see in low light as they are sensitive to picking up black
and white but not colors. - Cones pick up colors and function
best in bright light
- All the axons of the photoreceptor cells
bundle together and exit the eye at the
optic nerve - Because the optic nerve is made up of
the axons of the neurons in the eye and
not the actual photoreceptor cells of
the neurons, this forms the blind spot
which leaves a gap in our vision, but we
do not notice it because the brain fills it
in.
The Path to the Brain and Visual acuity.
The Pathway to the Brain
=The electrochemical signals follow a route from the optic nerve through to the occipital lobe in the back of the brain
= From the occipital lobe, the message may then be sent to other areas of the brain for further processing
Visual Acuity
=How well a person can see objects and distinguish between objects in the environment.
Color vision
Colour Vision
=Seeing color involves a combination of 3 factors:
- Hue – determined by the wavelength of
the light which Sternberg (2004) states that we see the shortest wavelength as violet and the longest as red. - Saturation – determined by how pure the color appears or how much it has been combined with white.
- Brightness – determined by the amplitude of the light wave, which is the amount of light we see coming from the wavelengths.
Visual Perception
-In order to make the visual world meaningful, the process of perception relies on the elements of the sensation that enters the brain, as well as memory,
past experience and the culture in which one lives
Processing of Visual Signals in the brain
- Visual signals are processed at different levels in the brain.
- Some regions deal with lower-level tasks and other regions with higher-level tasks.
u
-Primary visual areas, Secondary and tertiary visual areas.
Primary Visual Areas
- Lower-level or less psychologically complex areas that lie towards the top of occipital lobes.
- The input end of the brain’s visual system; the place where the more
elementary aspects of processing occur (such as perception of light intensity and edge detection)
Secondary and Tertiary Visual Areas
- Secondary visual areas – dedicated to a range of specialized visual processing tasks, such as the recognition of objects and color and motion processing.
- Tertiary visual areas – operate the most abstract and psychologically sophisticated aspects of visual processing.
- Possible effects of damage to these areas are an inability to calculate, to write, or to construct complex forms.
Perpetual constancy
Principles of perceptual constancy show that we use cues in the environment to keep our world predictable and stable
Colour constancy – this is when the perception of a color stays the same, although the image of it may change
Size constancy – this refers to the fact that, even though an object gets smaller on the retina as you get further away from it, you know its size remains the same
Shape constancy – this is when the shape of something changes on the retina, but you know its shape remains
the same
Depth Perception
The ability to perceive the three-dimensional quality of our world
We use both monocular and binocular cues from the environment to tell us about the depth
Form Perception
Gestalt psychologists explained a set of principles that we use in order to perceive our world visually
Principles state that we take the elements that make up an object and form a meaningful whole from them
- Proximity – those objects closest together are perceived as belonging together
- Similarity – things that look the same are grouped together
- Closure – people close or ignore the gaps in objects to form a meaningful whole
Gestalt Psychology
- Much of our understanding of how and why we perceive things comes from Gestalt Psychology
- For example - one of the most well-known Gestalt principles is the Phi Phenomenon, which is the illusion of movement from presenting stimuli in rapid succession. When you see a cartoon or running Christmas lights, you see movement (although none actually exists) because of this principle.
8 Gestalt Principles 1-2
- SIMILARITY refers to our tendency to group things together based upon how similar to each other they are. In the first figure above, we tend to see two rows of red dots and two rows of black dots. The dots are grouped according to similar colors.
- In the next figure, we tend to perceive three columns of two lines each rather than six different lines. The lines are grouped together because of how close they are to each other, or their PROXIMITY to one another.
8 Gestalt Principles 3-4
- CONTINUITY refers to our tendency to see patterns and therefore perceive things as belonging together if they form some type of continuous pattern.
In the third figure, although merely a series of dots, it begins to look like an “X” as we perceive the upper left side as continuing all the way to the lower right and the lower left all the way to the
upper right.
- The fourth figure, we demonstrate CLOSURE, or our tendency to complete familiar objects that have gaps in them. Even at first glance, we perceive a circle and a square.
8 Gestalt Principles 5-6
5) FIGURE-GROUND - this is the fundamental way we organize visual perceptions. When we look at an object, we see that object (figure) and the background (ground) on which it sits.
For example, when I see a picture of a friend.
6) SIMPLICITY/PRAGNANZ (good form) - we group elements that make a good form. However, the idea of “good form” is a little vague and subjective. Most psychologists think good form is
what ever is easiest or most simple.
For example, what do you see here: : > )
-Emoticons started
8 Gestalt Principles 7-8
7) COMMON FATE - elements that move together tend to be grouped together. For example, when you see geese flying south for the winter, they often appear to be in a “V” shape.
8) CLOSURE - we tend to complete a form when it has gaps.
Monocular depth cues
Depend on one eye only and are what most artists use in their artworks and include the following:
- Linear perspective – parallel lines, such as the rails of a railway track, look as though they move closer together
the further away they are - Patterns of light and shadow – these have been used by artists like Escher to create the perception of depth
- Relative size – if we see things that we know are similar in size, then we will know that the one that appears smaller
is further away - Motion parallax – things that are far away from you look as though they are moving more slowly than things that
are closer to you (Holt et al., 2012)
Binocular depth cues
- Binocular depth cues depend on both eyes and include the following:
1. Convergence – hold your finger in front of your face at arm’s length; look at your finger as you slowly move it towards your face; can you feel the muscles in your eyes start to tighten the closer the finger gets to your face?
Retinal disparity – as each eye picks up a different picture of the finger; when the images from both eyes are put together, depth perception occurs
Illusions and Perceptual deficits of Vision
Visual Illusions
- When we pick up signals from the environment and come to an incorrect perception.
- This is called illusion
- See examples of illusions
Perceptual Deficits of Vision
- Any deficit of perception is called an agnosia
- Visual-object agnosia occurs when people fail to recognize all types of visual objects
- Another agnosia is prosopagnosia where people cannot recognize faces (Sternberg, 2004)
- The patient cannot map the new perceptual experience of seeing someone’s face onto the memory they have for that person’s face
Perceptual Set
A perceptual set is….
-“a mental predisposition to perceive one
thing and not another”
-This is based on experiences, assumptions, and expectations.
What shapes our perceptual sets?
-What things do you think might affect
our perceptual sets
(i.e., our tendency to perceive things in
certain ways)?
- Context effects
- Past experiences
- Effects of our culture
Schemas
- Another word used to describe perceptual set is schemas.
- Schemas can influence our perception because we tend to see things that we expect to see. [opinion = you only see what you are looking for]
- We interpret things based on similar things we have experienced in the past –this is called assimilation.
When we experience something that’s not part of our schemas.
-Now what do you think would
happen if we receive new information that doesn’t fit our schemas?
-When we receive new information
we can ignore it (!)
- or we can change our schemas to fit the new information. This is called accommodation.
Schemas are almost like a box that we put information into. The way we organize compartments
in the box is based on things like our past experiences, contexts, etc. and this influences our perceptions
