Advanced cognitive psychology: Sensation and Perception

Sensation and Perception

Perceptual process_ Perception doesn’t just happen but is a end result of complex “behind the scenes processes which many don’t realize, this process is a sequence of processes that work together to determine our experience of and reaction to stimuli in the environment, the process is in four categories.
Stimulus Refers to what is out there in the environment and what we actually pay attention to and stimulates our receptors.
Electricity refers to the electrical signals that are created by the receptors and sent to the brain.
Experience and action Refers to our goal-to perceive, recognize and react to the stimuli

Knowledge refers to the knowledge we bring to the perceptual situation

The Stimulus- It can exist external and internal to a person

Environmental stimuli and attended stimuli: Environmental stimulus is all the things in ur environment that we can potentially perceive. If someone is walking through the woods there is far too much happening at once for someone to take in so they look place to place scanning the environment for something to catch their interest, for example a certain tree, she doesn’t notice the pattern of the trunk first and realise the patch of moss it actually a moth, this becomes the attended stimulus and this changes moment to moment as the person shifts their attention place to place.

The stimulus on the receptors:  When the attention is directly on the moth, she looks directly at it, this creates an image of the moth on the retina of the eye and this counts as a representation of the moth as it’s not the actual moth.

Electricity

Transduction- this is the transformation of one form of energy into another form of energy, this occurs in the nervous system when energy in the environment such as light energy is transformed into electrical energy such as the image of the moth in the retina is transformed into electrical signals in thousands of the visual receptors.

Transmission- After the moth’s image has been transformed into electrical signals in the receptors, these signals activate other neurons which in turn activate more neurons and eventually these signals leave the eye and transmit to the brain and this is crucial because if it doesn’t reach the brain there is no perception.

Processing- AS the signals are transmitted they undergo Neural processing  Which involves interactions between neurons. The image of the moth is changed into electrical signals in the receptors, which eventually are sent out the back of the eye. This signal which represents the moth , is relayed through a series of neurons to the brain, which transforms this signal into a perception of the moth, the signal that reaches the brain is transformed so that it represents the original stimulus however it can be very different from the original signal, this transformation between receptors and brain is achieved by neural processing, which happens as the signals that originate in the receptors travel through a maze of interconnected pathways between the receptors and the brain  and within the brain.

Experience and action- This is where the unaware things going on transform into things we are aware of-perceiving, recognizing, and acting on objects in the environment.

Perception is conscious sensory experience. It occurs when the electrical signals that represent the moth are transformed by the brain into her experience of seeing the moth. She has perceived the moth but other things have happened as well such as recognizing the form of the moth. There are two addition steps,

Recognition this is the ability to place the object in question into a category such as a ‘moth’ , that gives it a meaning. Although we might be tempted the group perception and recognition together researchers have shown they are two separate things such as the Dr P study where he could perceive the object such as a glove he described it as a container showing he has perceived the object however unable to attach the meaning of a glove to it.

Action This includes motor activities such as moving the head or eyes and scanning the environment such as looking at the moth and moving directly towards it and researchers see this is an important outcome because of its importance for survival. David Milner and Melvyn Goodale (1995) say that early in evolution the main goal of visual processing was not to create a conscious picture but to help animal control navigation. Perception often leads to action such as a animal increasing its vigilance when hearing a twig snap or a person’s deciding to look more closely at something that’s interesting shows that perception is a continuously changing process.

Knowledge: is any information that the perceiver brings to the situation, it can affect a number of steps in the perceptual process, it can be things learned from years ago such as learning the difference between a moth and a butterfly and events that have just happened such as perceiving as picture –mouse or a guy test-.

There is another way to describe the effect of information is by distinguishing between bottom-up processing and top-down processing, bottom up processing  is processing that is based on incoming data, this always provides a starting point for perception because without incoming data there is no perception. The incoming data are the patterns of light and dark on her retina created by light reflected from the moth and the tree. Top-down processing refers to processing that is based on knowledge such as what they know about moths. Knowledge isn’t always involved in perception but it often is and sometimes without even being aware of it.

Bottom up processing is essential for perception because the PP usually begins with a stimulus of the receptors. Such as a pharmacist reads a unreadable scribble on a doctors prescription she starts with the patterns that the doctors handwriting creates on her retina, top-down processing can also work as well such as past experience with this particular handwriting therefore both approaches work together to create perception.

Usually very simple stimuli don’t use TD processing.

How to approach the study of perception
The Psychophysical approach  Was in introduced by Gustav Fechner who coined the term psychophysics to explain the relationship between the stimuli and perception, and these methods are still used today.an example to measure the stimulus-perception relationship would be asking a observer to decide whether two very similar patches of colour was the same or different

The physiological approach involves measuring the relationship between stimuli and PP and PP and perception and these psychological responses are often studied by measuring electrical responses in the nervous system but can also involve studying anatomy or chemical processes an example would be measuring how different coloured lights result in electrical activity generated in neurons in a cat’s cortex and basic brain activity.

Both approaches work toward a common goal-to explain the mechanisms responsible for perception, every time we measure physiological responses the aim is to see how neurons and the brain create perceptions, the knowledge and top down processing part of this is known as the cognitive influences on perception. Both approaches provide information about different aspects of the process and to truly understand it we have to use both.

Measuring perception;

Description: When a researcher asks a person to describe what they perceive they are using a phenomenological method. This is the first step because it describes what we perceive; this is where the study of perception begins because these are the basic properties that we are seeking to explain

Recognition:  When we categorize a stimulus by naming it, we are measuring recognition, often for treating people with brain damage such as Dr P with the glove etc.

Detection: in Gustavs Fechner’s book he described a number of quantitive methods and these were known as classical psychophysical methods because they were the original methods used to measure the P-S relationship

The absolute threshold is the smallest amount of S energy necessary to detect a stimulus e.g. the smallest amount of light that makes a person detect it would be the AT for that.

The difference threshold is the smallest difference between two stimuli that a person can detect, Weber found that when the difference between the standard and comparison weights are small the observers found it difficult to detect a difference in the weights but large differences easier, also as the magnitude of the stimulus increases so does the size of the DL, the relationship based on Webers research but stated mathematically by Fechner was DL/S _ K and was called Webers law. K is a constant called Weber fraction, S is the value of the standard stimulus. Numerous tests have shown this law to be true in most cases if the stimulus intensity is not too low. The weber fraction remains relatively constant for a particular sense. His proposal of 3 psychophysical methods of measuring and the law were important events because it showed mental activity could be observed quantitively however did not measure things about threshold perceptions.

Magnitude Estimation: If we double the intensity of a tone, does it sound twice as loud? In 1957 S.S. Stevens developed a technique called scaling or magnitude estimation that accurately measured this relationship. The results from the test show that doubling it does not double the perceived brightness, e.g. when intensity is 20 the perceived is 28 and when we double intensity to 40 the perceived only increases to 36, this is called response compression, they both increases but not at the same rate. The results for the sensation for electric shock presented to the finger and for the perception length of a line. The electric shock curve bends up indicating that doubling the strength of a shock more than doubles the sensation of being shocked, increasing the intensity from 20 to 40 made the shock sensation from 6 to 49, this is called response expansion and for the line test the things matched identically. The relationship between intensity of a stimulus and our perception of its magnitude follows the same general equation for each sense. These functions are called Power functions and are described by the equation P _ KSn. and is known as Stevens power law.

Search: This method is where participants are asked to find one stimulus amongst other quickly as possible, we will see that measuring reaction time, the time between presentation of the stimulus and the observer’s response to the stimulus has provided important information about mechanisms responsible for perception