Illusions are experiences of perception in which one perceives stimuli incorrectly, not completely, or in distorted way. Some are caused by external factors (unrelated to the receiver's sensory organs and brain), as in the case of the “Doppler effect”, when one hears, say, the siren of an ambulance change its pitch as it passes by when, in reality, the pitch stays the same. The ears and brain of the receiver function normally, but this function is impeded by external natural factors like distance, interference of elements in the air, wind and its direction, etc. Illusions of this kind are called stimulus-distortion illusions . Other illusions are more receiver-related, and are referred to as perceiver-distortion illusions . These are caused by the way in which the human brain functions and, in particular, its tendency to group similar objects together as well as to “complete” unfinished objects. The latter function is what makes watching a movie possible, since it “blocks” perception of the intervals between projected stills and makes them look like a “moving” picture.

Researchers have designed various optical perceiver-distortion illusions. Some of the best known are the “figure and ground” illusion, occurring when looking at a white illustration on a solid black background; the Müller-Lyer illusion, where two equally long straight lines feature inward and outward arrow-shaped ends which make them look unequal; the Zöllner illusion, in which long parallel lines look as if they tend to intersect by means of other, shorter lines which do intersect them, and the Ponzo illusion, where two equal circles are placed inside an acute angle, resulting in the circle located closer to the angle's top giving the impression of being larger.

Much more interesting than these optical party tricks are illusions brought about by intersensory effects . Normally, the senses cooperate and enhance the experience of perception. The experience of a pleasant moment at the seaside, for instance, comprises visual experience, like the brightness of the sky and the color of the sea, auditory experience, like the sound of the waves lapping on the shore and the voices of other people, perhaps even experience of smell, perceiving the fresh, salty aroma of the sea. All senses combine to contribute to the enjoyment of the experience. There is a condition, however, called synaesthesia , where this intersensory cooperation becomes confused. In such cases, sounds and smells are often reported to carry the visual sensation of color, or certain words to produce musical tones. Synaesthesia is not to be confused with the manner in which a certain experience might strongly remind us of another. Rather, people who have it actually experience an additional sense when they perceive certain stimuli. It is often a symptom of various psychiatric disorders and, in extreme cases, one is unable to distinguish between sight and sound.

Which of the following is a correct account of the Doppler effect?

Question

Illusions are experiences of perception in which one perceives stimuli incorrectly, not completely, or in distorted way. Some are caused by external factors (unrelated to the receiver's sensory organs and brain), as in the case of the “Doppler effect”, when one hears, say, the siren of an ambulance change its pitch as it passes by when, in reality, the pitch stays the same. The ears and brain of the receiver function normally, but this function is impeded by external natural factors like distance, interference of elements in the air, wind and its direction, etc. Illusions of this kind are called  stimulus-distortion illusions . Other illusions are more receiver-related, and are referred to as  perceiver-distortion illusions . These are caused by the way in which the human brain functions and, in particular, its tendency to group similar objects together as well as to “complete” unfinished objects. The latter function is what makes watching a movie possible, since it “blocks” perception of the intervals between projected stills and makes them look like a “moving” picture.

Researchers have designed various optical perceiver-distortion illusions. Some of the best known are the “figure and ground” illusion, occurring when looking at a white illustration on a solid black background; the Müller-Lyer illusion, where two equally long straight lines feature inward and outward arrow-shaped ends which make them look unequal; the Zöllner illusion, in which long parallel lines look as if they tend to intersect by means of other, shorter lines which do intersect them, and the Ponzo illusion, where two equal circles are placed inside an acute angle, resulting in the circle located closer to the angle's top giving the impression of being larger.

Much more interesting than these optical party tricks are illusions brought about by  intersensory effects . Normally, the senses cooperate and enhance the experience of perception. The experience of a pleasant moment at the seaside, for instance, comprises visual experience, like the brightness of the sky and the color of the sea, auditory experience, like the sound of the waves lapping on the shore and the voices of other people, perhaps even experience of smell, perceiving the fresh, salty aroma of the sea. All senses combine to contribute to the enjoyment of the experience. There is a condition, however, called  synaesthesia , where this intersensory cooperation becomes confused. In such cases, sounds and smells are often reported to carry the visual sensation of color, or certain words to produce musical tones. Synaesthesia is not to be confused with the manner in which a certain experience might strongly remind us of another. Rather, people who have it actually experience an additional sense when they perceive certain stimuli. It is often a symptom of various psychiatric disorders and, in extreme cases, one is unable to distinguish between sight and sound.

Which of the following is a correct account of the Doppler effect?

Answer

One variable auditory stimulus sounds different due to external, natural factors.

Answer

One unchanging auditory stimulus sounds different due tothe function of the brain.

Answer

One variable auditory stimulus sounds different due tothe function of the brain.

Answer

One unchanging auditory stimulus sounds different due to external, natural factors.

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Illusions are experiences of perception in which one perceives stimuli incorrect...

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