CH9 Perception

Sensory receptors in the sense organs detect and respond to light, sound and chemical energy.

Sensation: an automatic physical reaction to a stimulus that is the same for everyone.

• Sensation is a process that involves three stages:
• 1.reception
• 2.transduction 
• 3.transmission.

Reception: Detection of stimulus energy by sensory receptor cells of the various sense organs.

Transduction: Converting stimulus energy into electrochemical energy that can be transmitted to the brain as neural impulses

Transmission: sending the information form receptor sites to through neural pathways to specific sensory areas in the brain

Perception: a psychological activity that gives meaning to the stimuli our sense organs detect.

• Perception involves three stages:
• 1.selection
• 2.organisation
• 3.interpretation

Selection: the process of attending to certain sensory stimuli and excluding others.

Organisation: the process of regrouping sensory stimuli to form a meaningful whole or pattern.

Interpretation: the process in which information is given meaning to that it can be understood.

Bottom-up processing: when our sensory receptors, such as our eyes, receive sensory information and we do not rely on prior experience in order to interpret it.

Builds knowledge in real-time as the stimuli are received, allowing each of the lements to be perceived.

Top-down processing:  used when the brain starts with an overall hypothesis about a stimulus and uses context and general knowledge to fill in any blanks.

Uses prior knowledge to fit the incoming stimuli with similar previous understandings.

Attention: a voluntary (conscious) or involuntary (unconscious) tendency to focus awareness on a specific stimulus and ignore other stimuli.

Controlled processes: conscious, voluntary actions or cogntive processes that require a high level of attention and monitoring

Automatic processes: actions that require little conscious awareness or mental effort, and do not interfere with performance on other activites.

Sustained attention: focusing attention on an activity or stimulus over a prolonged period without being distracted by other stimuli.

Allows us to fully process information or complete a task 

e.g. watching a movie without pausing or going back to understand the plot

Divided attention (often referred to as multitasking): refers to rapidly switching the focus of your awareness between two (or more) sources of information so you can perform two (or more) tasks at the same time.

Allows us to process mutliple sources of information or stimuli more effeciently

e.g. driving while following directions from navigation system

Selective attention: choosing to focus your awareness on a specific or limited range of stimuli while ignoring other stimuli.

Acts as a filter that helps us to prioritise incoming information according to its importance

e.g. focusing on what one person says and ignoring sounds of other conversations

Visual perception is the process of becoming consciously aware of visual stimuli as a result of the interactions between the visual sensory system, and the individual’s internal and external environments.

Biological factors: physical, physiological, neurological or genetic factors that are entirely internal.

Depth perception: ability to see three-dimensional space and accurately judge distances using environmental cues.

Binocular cues: depth cues that require both eyes to work together and provide the brain with information about depth and distance.

• Two binocular depth cues:
• 1.Retinal disparity
• 2.Convergence

Retinal disparity: is a depth cue created by small differences between the image that reaches the right eye and the image that reaches the left eye

Convergence: involves both eyes simultaneously turning inwards as an object moves closer (within approximately 7m) in order to maintain focus on the object .

Monocular cues: depth perception cues that rely on information from only one eye. 

• Two types of monocular depth cues:
• 1.Accommodation
• 2.Pictorial cues

Accommodation: the changing shape of the lens to maintain focus on objects of varying distances.

• When the object is close the lens is more rounded.
• When the object is further away the lens flattens

Pictorial cues: monocular cues present in two-dimensional (pictorial) images that allow the brain to perceive apparent three- dimensional depth.

• Types of pictorial cues:
• Linear perspective
• Relative size
• Interposition (overlap)
• Texture gradient
• Height in field

Linear perspective: The apparent convergence of parallel lines creates the impression of increasing distance.

The relative size of objects to one another in our visual field helps us to judge distance.

e.g. If two similar objects cast different sized images on the retina, the object that casts the larger image is perceived to be closer, and the one that cast a smaller image is perceived to be further away.

Interposition (also known as overlap): When one object partially blocks another object it is perceived as being in front of and, therefore, closer than the object it covers

Texture gradient: We rely on the use of texture to judge how far away objects are. The closer we are, the greater the detail of texture we can see.

e.g. When looking at a field up close, we can make out the individual blades of grass or flowers. The further away the field is, the less details we can see.

Height in the visual field: In our visual field, the closer objects are to the horizon line, the further away they appear. This means that their height in the visual field helps us to determine their distance.

Visual perception principles: rules the brain applies automatically to organise and interpret visual stimuli in a consistent and meaningful way.

Gestalt principles: rules used to organise separate elements of a visual stimulus into meaningful patterns or whole forms.

• Figure ground 
• Closure
• Similarity
• Proximity

Figure–ground: applying an imaginary contour line to perceptually group and separate some features of a stimulus so that a part of the stimulus appears to stand out as an object (the figure) against a plainer background (the ground).

Camouflage is used to break up the contour of the figure, meaning the figure and ground will blend.

Closure: tendency to perceptually complete an incomplete figure by filling in an imaginary contour line so that the figure has a consistent overall form.

• The tendency to perceive stimuli that have similar visual features
• (e.g. size, shape, colour or form) as belonging together and forming a meaningful whole.

The tendency to perceive stimuli that are close together in space as belonging together and forming a meaningful whole.

Visual constancies: perception principles that allow us to view objects as unchanging in terms of their actual size, shape, brightness and orientation, even when there are changes to the image that the object casts on the retina.

Size constancy involves recognising that an object’s actual size remains the same, even though the size of the image it casts on each retina changes.

Shape constancy is the tendency to perceive an object as maintaining its shape despite the changing perspective from which it is observed.

Brightness constancy is our tendency to perceive an object as maintaining it’s level of brightness in relation to it’s surroundings, despite changes in the amount of light being reflected from the object onto the retina.

An object’s true orientation (position) is perceived as being unchanged despite changes in the orientation of the object’s image on our retina

Context: refers to information (conditions or circumstances) that surrounds a stimulus that influences the perception of the stimulus.

Motivation: an internal state that activates, directs and sustains behaviour in relation to achieving a specific goal. Motivation can be either conscious or unconscious. It can influence how we interpret the world around us.

Culture: all the distinctive beliefs, values, customs, knowledge, art and language traditions that provide the basis of everyday social behaviours and that are handed down from one generation to the next

Taste (gustation): the sensory experience of food or drink that is put into the mouth and perceived as flavour.

• Genes
• ​Age

Genetic make-up influences the amount of and composition of gustatory receptors on taste buds. 

Research suggests that taste and general eating behaviour, including meal size and calorie intake, are controlled by our genes.

e.g.Twin studies have found links between genetic make-up, taste perception and preference for proteins, fat and carbohydrates.

Age can effect taste preferences and sensitivity. As we age, the number of taste buds and their sensitivity decreases, impacting a person's flavour perception as their ability to discriminate between tastes is weakened.

Visual illusion: a consistent misinterpretation of a visual stimulus.

Agnosia: a disorder involving the loss or impairment of the ability to recognise familiar stimuli through the use of one or more senses, despite the senses functioning normally otherwise.

A person with visual agnosia can see, but they cannot interpret what they see.

Apperceptive visual agnosia: occurs due to impairment at the first stage of visual processing.

It is the inability to recognise visual stimuli such as shapes or forms of an object despite having no visual deficits.

Associative visual agnosia: occurs due to impairment to the second stage of visual processing.

It is the inability to recall information associated with an object, such as its name or what it is used for.

Prosopagnosia (also known as face blindness): is the inability to recognise familiar faces (sometimes their own) or facial differences, and they cannot identify a person by name.

Supertasters are born with more taste buds and taste receptors on their tongue than average, and so have a higher taste sensitivity

Miraculin: a type of protein extracted from the ‘miracle berry’ which alters taste perception in humans.

When consumed with something sour, turns the sour tasting food or drink into a sweet-tasting food or drink.

Synaesthesia: refers to a group of neurological conditions where information taken in by one sense is involuntarily experienced in a way normally associated with another sense.

Spatial neglect: a cognitive impairment where affected people fail to pay attention to, recognise or respond to stimuli located on one side of their body or in their visual space.