EP - S4 Perception / Geometric Illusions

What is perception?

The way sensory information is organized

What is sensation?

The physical process of detecting stimuli through sensory receptors (e.g. smelling cinnamon).

What is the difference between sensation and perception?

Sensation is the physical detection of stimuli; perception is the psychological interpretation of those stimuli.

What is bottom-up processing?

Perceptions built directly from sensory input; data-driven processing.

What is top-down processing?

Perception guided by knowledge

What is sensory adaptation?

Diminished sensitivity to constant or unchanging stimuli over time (e.g. not hearing a clock tick after a few minutes).

What is attention?

The process of focusing conscious awareness on a particular stimulus; gates what moves from sensation to perception.

What is inattentional blindness?

Failure to notice a fully visible object because attention is focused elsewhere (e.g. the gorilla video).

What was the gorilla video demonstration?

Viewers counting basketball passes often fail to notice a person in a gorilla suit walking through the scene for nine seconds. Demonstrates inattentional blindness.

What is signal detection theory?

A framework separating perceptual sensitivity from response bias; perception involves both evidence and decision processes influenced by costs and benefits.

How does motivation affect perception according to signal detection theory?

Motivation shifts the response criterion. Expecting an important phone call lowers the criterion making false alarms more likely. A mother wakes to a baby's murmur but not to other sounds.

What is the Müller-Lyer illusion?

An optical illusion where two lines of equal length appear different because of arrow-like fins at the ends. The line with inward-pointing fins appears longer; outward-pointing fins appear shorter.

What is the Sander Parallelogram illusion?

A geometric illusion where the diagonal of a parallelogram appears longer than the side of the parallelogram though they are actually equal.

What is the Horizontal-Vertical illusion?

An illusion where a vertical line appears longer than a horizontal line of the same length. More pronounced in people from open flat terrains.

What did Segall Campbell and Herskovits (1963) find about the Müller-Lyer illusion across cultures?

European samples (Evanston; Johannesburg) showed greater susceptibility to the Müller-Lyer illusion than non-European samples. Supports empiricist (learned) view of perception.

What did Segall et al. find about the Horizontal-Vertical illusion across cultures?

Non-European samples showed greater susceptibility to the Horizontal-Vertical illusion than European samples. Suggests different visual inference habits from different ecological environments.

What is the "carpentered world" hypothesis?

The hypothesis that people from environments with many right angles and rectangular buildings learn to interpret acute and obtuse angles as representing 3D rectangular corners which enhances the Müller-Lyer illusion.

What is the empiricist view of perception?

Perception involves learned habits of inference that develop in response to cultural and ecological factors in the visual environment. Illusion susceptibility is not innate but learned.

What is the nativist view of perception?

The view that perceptual abilities are innate (present at birth) rather than learned through experience. Segall's cross-cultural differences challenge strong nativist views.

What is the point of subjective equality (PSE) in the Segall study?

In psychophysics the stimulus value at which a person perceives two stimuli as equal (e.g. the percentage discrepancy at which the two lines in an illusion appear equal).

What is a psychophysical ogive?

A graph showing the proportion of "illusion-produced" responses as a function of percentage discrepancy; used to determine the point of subjective equality.

What is the Stroop effect?

Interference in naming the color of a word when the word itself spells a different color (e.g. the word "RED" printed in blue ink). Demonstrates automatic processing of reading.

What are the two theories explaining the Stroop effect?

Speed of Processing Theory (words are read faster than colors are named) and Selective Attention Theory (naming colors requires more attention than reading words).

What is an example of top-down processing?

Believing that a reduced-fat food will taste good because of positive attitudes toward reduced-fat products; the belief shapes the taste perception.

What is an example of bottom-up processing?

Detecting the smell of cinnamon through scent receptors without any prior expectation or context.

What is the relationship between beliefs and perception?

Individuals who hold positive attitudes toward reduced-fat foods rate those foods as tasting better than people with less positive attitudes.

What is the significance of the Segall et al. (1963) study for psychology?

It provided strong cross-cultural evidence that perception is influenced by learning and environment challenging the universality of visual illusions and supporting the empiricist position.

What are the two orthogonal factors that emerged from Segall et al.'s factor analysis?

Factor 1: Müller-Lyer and Sander parallelogram illusions loaded together. Factor 2: Horizontal-vertical illusions loaded together. Different cultural patterns for each factor.

What is the relationship between open flat terrain and the Horizontal-Vertical illusion?

People from open flat environments (e.g. savannas) learn to interpret vertical lines as extensions away in the horizontal plane enhancing the illusion. People from dense forests (e.g. rainforests) show less of this illusion.

What is a Guttman error in the Segall study?

An inconsistent response pattern where a person gives an illusion-produced response to a larger percentage discrepancy item but a non-illusion response to a smaller percentage discrepancy item within the same figure set.

What is the Scheffé procedure?

A conservative statistical method for making multiple non-independent comparisons while controlling for Type I error rate. Used by Segall et al. to compare many cultural groups.

What is an example of sensory adaptation in daily life?

Entering a classroom with an old analog clock: you hear the ticking at first but after a few minutes of conversation you are no longer aware of it.

What is an example of inattentional blindness?

At a party focused on a conversation you fail to notice a song that just finished playing or a person in a gorilla costume walking through the room.

What is the difference between bottom-up and top-down processing?

Bottom-up is driven by sensory input (data-driven). Top-down is driven by knowledge and expectations (conceptually-driven).