Psychology AOS 2 - Distortions in Perception: Chapter 9

Perceptual distortion

Inconsistency between perceptual experience and physical reality. Happens because of a mistake or distortion in perception.

Visual illusion

Misperception of external visual stimuli, occurring due to a distortion or mistake when interpreting the stimuli. Every time we view the illusion, we have the same sensory experience.

What do visual illusions demonstrate about the brain's perceptual role?

That the brain has an important role in constructing our view of the world, and also that perceptual principals like past experience, learning and context have a strong effect on the formation of perceptions.

What are the 3 main visual illusions?

> Muller-Lyer Illusion

> Ames room

> Spinning Dancer Illusion

Müller-Lyer illusion

Named after Franz Müller-Lyer in 1889, it is a visual illusion in which one of two lines of equal length, each of which has opposite shaped ends, is incorrectly perceived as being longer than the other.

3 explanations for Müller-Lyer illusion

1. Incorrect depth and distance cues when judging 2D objects

2. Carpentered World Hypothesis - illusion is similar to familiar architectural features so the two lines seem to be at different distances from us. A critique is that the illusion still works without the pointed ends

3. Ross Day theory - Visual cues of image contradict each other and give conflicting information, leading us to make a perceptual compromise to choose 'best sense' option

Ames room illusion

Perceptual misinterpretation where a trapezium-shaped room appears rectangular when viewed through monocular peephole, and distorts size perception.

Size constancy

We maintain a constant idea of an object's size, even though its size on the retina changes

Shape constancy

Objects are perceived to maintain their known shape despite changing perspective from which it's observed. This is a learned skill, as a toddler may struggle to recognise a toy from a different angle.

Ames room explanation

Brain assumes room is rectangular, drawing on shape constancy, and we misjudge depth and size, leading people to appear to grow and shrink. Windows and clocks also act as size and shape cues, and the hindrances of monocular vision are utilised.

It shows we maintain shape constancy over size constancy

Spinning Dancer Illusion

Dancer's silhouette can appear to spin either direction

Spinning Dancer Illusion explanation

Lack of depth cues mean it is unclear which side of the body is closest. Most commonly perceived to be spinning clockwise.

Agnosia

Loss or impairment of recognition for objects, persons, sounds, or other sensory stimulus using one of more senses despite otherwise functioning senses.

Visual agnosia

Loss of impairment of ability to recognise visual stimuli, particularly with familiar objects and faces. These difficulties are unrelated to sight, memory loss or language

Visual Agnosia types

Apperceptive, associative, prosopagnosia, simultanagnosia, topographical, colour, agnosic alexia

Apperceptive visual agnosia

An inability to accurately perceive visually presented stimuli. What is seen cannot be recognised. Can’t put separate elements into a whole, but can identify with other senses. Unlikely to be able to draw, copy or match a picture. Similarities with blindness

Associative Visual Agnosia

Inability to associate a visual stimulus with stored information about objects in memory despite having otherwise normal perceptual abilities. Can describe object or draw it, but can't say what it is or its use.

Prosopagnosia

An inability to recognise a familiar face, including their own when seen in a mirror or photograph. Other visible characteristics like tattoos can help recognition. In a mirror, they don't recognise themselves but know it must be them as they are the only one in the reflection.

Simultanagnosia

An inability to recognise more than one object at a time in a scene that contains more than object. When looking at 2 items, only 1 perceived, and when attention shifts they no longer 'see' previous object.

Topographical Agnosia

An inability to find one's way around familiar environments. Difficulties using visual cues to guide.

Colour Agnosia

An inability to identify and distinguish between different colours, despite normal basic colour vision and colour discrimination mechanisms.

Agnosic Alexia

An inability to recognise or comprehend written or printed words. Word blindness or 'pure alexia'. Talking, writing and listening are unaffected.

Visual Agnosia Cause

Rare disorder in 1% of those with brain damage, caused by stroke, traumatic brain injury, tumour, exposure, dementia, etc. Ventral stream involved in visual recognition is damaged which connects Primary Visual Cortex in Occipital lobe with the temporal lobe.

Agnosia Treatment

Methods to solve underlying cause such as tumour, and rehab to teach compensatory recognition through other senses

Synaesthesia

Perceptual experience where stimulation in one sense produces additional sensations in another. It is usually just one-way, not bidirectional.

Synaesthesia types

Grapheme-Colour - sees colour viewing words, numbers or symbols

Word-gustatory

Auditory-tactile

Mirror-touch - You feel touch when you see others touched

Pain - Experience pain when you see others experience it
Time-space

Chromesthesia - non-visual stimuli accompanied by colour

Chromatic-audition - Colours experienced when sounds heard

Synaesthesia characteristics

- Real experience

- Involuntary, automatic and difficult to suppress

- Vivid, memorable, consistent

- Same colour/feeling/etc experienced for relevant sensory experience

- One way

- More common in women

Synaesthesia causes

Possibly a Neurological, inherited condition, or high sensory sensitivity, or a lack of neural pruning in development leading to an overabundance of neurons

Spatial neglect

A neurological disorder where individuals can't notice things in a visual field even though there may be no sensory loss. They tend to behave as if that one side of their world does not exist. Patients are unaware of their disorder.

Most common in visual sense, and can vary greatly in intensity

Spatial neglect cause and common area of damage

Stroke or accident victims with fairly extensive injury to the cerebral cortex in the rear area of the parietal lobe of the right hemisphere. They consequently usually ignore the left visual field.