4.1—sensation and perception Flashcards
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4.1 Learning Objectives
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4.1 Focus Questions
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Sensation
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the process of detecting external events by sense organs and turning those stimuli into neural signals.
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Perception
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involves attending to, organizing, and interpreting stimuli that we sense.
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Transduction
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- transduction: when specialized receptors transform the physical energy of the outside world into neural impulses.
- raw sensations detected by the sensory organs are turned into information that the brain can process through transfuction.
- this ultimately gives rise to our internal representation of the world.
- all of our senses use the same mechanism for transmitting information in the brain: the action potential.
- in order to separate different sensory signals from one another so that we can experience distinct sensations, the brain sends signals from different sensory organs to different parts of the brain.
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Doctrine of Specific Nerve Energies
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- doctrine of specific nerve energies: first proposed in 1826 by the German physiologist Johannes Müller; the idea that different senses are separated in the brain.
- these pathways are built through experience.
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Sensory Adaptation
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- sensory adaptation: the reduction of activity in sensory receptors with repeated exposure to a stimulus.
- unchanging stimuli elicit less activity in the nervous system, and are percieved as being less intense over time.
- e.g. directors changing camera angles so that your brain can’t adapt and will keep hold of your attention.
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Psychophysics
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- psychophysics: the field of study that explores how physical energy such as light and sound and their intensity relate to psychological experience
- e.g. how much perfume would need to be spilled in a three-you apartment for you to detect the odour?
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Absolute Threshold
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- absolute threshold: the minimum amount of energy or quantity of a stimulus required for it to be reliably detected at least 50% of the time it is presented.
- this varies among individuals (and species) and across the life span.
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Difference Treshold
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- difference threshold: the smallest difference between stimuli that can be reliably detected at least 50% of the time.
- e.g. adding one pinch of salt to fries with no salt will create a different taste from adding one pinch of salt to fries that already have four pinches of salt.
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Stimulus Threshold Limitations
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- the study of stimulus thresholds has its limitations.
- whether someone perceives a stimulus is determined by self-report—an individual reporting that she either did or did not detect a stimulus.
- not all people are equally willing to say they sensed a weak stimulus; some will wait until they’re 100% certain.
- e.g. real-world implications: radiologist trying to detect tumours in a set of images.
- if there are differences in the absolute threshold of different radiologists, then one might miss tumours that the other would have detected.
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Signal Detection Theory
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- signal detection theory: whether a stimulus is perceived depends on both sensory experience and judgment made by the subject.
- sensory process: signal detection experiment conducted in the laboratory, the experimenter presents either a faint stim- ulus or no stimulus at all.
- decision process: subject is asked to report whehter or not a stimulus was actually presented.
- hit: correct that you heard a sound.
- correct rejection: correct that you didn’t hear a sound.
- false alarm: think you heard something that’s not there.
- miss: fail to detect that a stimulus was presented.
- by analyzing how often a person’s responses fall into each of these four categories, psychologists can accurately measure the sensitivity of that person’s sensory systems.
- motivational changes are likely to affect your decision process, changing your sensitivity. (i.e. you’re more likely to hear a bear growl or twig snap on your own at night in the woods than with friends hiking.)
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Subliminal Messaging
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- we can perceive subliminal stimuli under strict laboratory conditions.
- subliminal perception can occur, and it can produce small effects in the nervous system.
- claims that subliminal perception can influence behaviours may be inaccurate.
- e.g. Greenwald study
- even if changes were to occur after a subject heard subliminal tapes, these effects may be due to the participants’ expectations.
- people were given two sets of tapes (e.g. a memory cassette with memory label, and a memory cassette with a self-esteem label).
- participants experienced improvement based on the labels, and not what they actually heard.
- subliminal messages are unlikely to create motivations that hadn’t previously existed.
- therefore, it’s definitely not a form of mind control.
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Gestalt Psychology
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- Gestalt psychology: “the whole is greater than the sum of its parts.”
- figure-ground principle: objects or “figures” in our environment tend to stand out against a background.
- proximity; we tend to treat two or more objects that are close in proximity to each other as a group.
- similarity; experienced by viewing groups of people in uniform.
- continuity: “good continuation”; lines and other objects tend to be continuous, rather than abruptly changing direction.
- closure: the tendency to fill in gaps to completely a whole object.
- Gestalt concepts are not simply a colelction of isolated examples; they demonstrate how we create our own organized perceptions out of the different sensory inputs that we experience.
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Phonetic Reversal
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- in 1985, two teens committed suicide (one lived), claiming their actions were influeced by “subliminal messages” found in the heavy metal music by Judas Priest.
- the family sued the band, claiming that when played backwards, the song “Better by You, Better Than Me” contained the phrase “do it.”
- most examples of backward messages are due to phonetic reversal: where a word pronounced backwards sounds like another word.
- after this, John Vokey and Don Read (in 1985) conducted experiments about backwards messages.
- when asked to make judgments about the con- tent of the backward messages, participants’ performance fell to chance levels.
- they were unable to distinguish between nursery rhymes, Christian, satanic, pornographic, or adver- tising messages (19.1% correct, where chance performance is 20%)
