9A Errors of sight - PSYCH

Fallibility

The quality of being prone to error or experiencing difficulties in judgement.

Perceptual distortions

An error in the judgement or interpretation of sensory stimuli

Visual illusion

The perception of a visual stimulus that conflicts with how it is in physical reality.

Muller-lyer illusion

Carpentered world hypothesis: Suggests that when we see the plain two-dimensional lines of the illusion, we automatically apply them to real three-dimensional objects in our world stored in our memory, such as the corners of the room and buildings.

It found that people who lived in cities were more susceptible to the illusion than people that lived in more rural areas.

The Ames room illusion

The room’s design purposefully manipulates certain visual cues in order to impair a viewers ability to correctly apply visual constancies.

• Size constancy: A person standing on the left actually looks to be shrinking as they get further away. Normally, our brains would allow us to see a change in size like this as a change in distance, and therefore it would not affect our perception of a person’s true size compared to the image of them cast onto our eyes. However, because the room is deceptively disguised, we are unable to see their change in distance and are therefore unable to apply size constancy.

• Shape constancy: We are also likely to misinterpret the shape of the room. We see the room as maintaining a constant rectangular shape when viewed through the peephole because we are unaware that the room is a trapezoid.

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.

Apperceptive visual agnosia

• Difficulty in perceiving visual information

• Intact mental understanding of what objects look like

• Inability to identify objects is caused by a difficulty in perceiving the form or visual elements of an object

• Otherwise normally functioning vision

Associative visual agnosia

• Difficulty in identifying what object is being viewed

• No difficulty in perception, individuals are able to identify the individual visual elements of an object

• Identification difficulties stem from being unable to link prior experience to the object they are viewing

• Otherwise normally functioning vision

Similarity and difference between apperceptive and associative visual agnosia

One similarity between people who experience apperceptive and associative visual agnosia is that they both experience a difficulty in identifying or categorising objects.
However, individuals with apperceptive visual agnosia cannot identify objects due to difficulties in perceiving visual elements in a object, whereas individuals with associative visual agnosia cannot identify objects due to an inability to link prior experience to the object they are viewing.