Introduction to sensation and perception

Introduction to Sensation and PerceptionChapter 4

How Psychology developed as a field.The ways Psychologists conduct research.The basic building blocks.Genes, Nervous System, HormonesBringing the world into your brain.Sensation and PerceptionChapter 1 –Chapter 2 –Chapter 3 –Chapter 4 –

Why Study Sensation and Perception?“I’ll believe it when I see it”“I know what I saw (heard)”“How can you eat that!!”“What do you mean, you like getting spanked?”

Each of these, at least at the most basic level, involves sensation and perception.

Two Main PointsHuman sense organs are not like electronic equipmentEyes are not cameras, Ears are not microphones…There is variability in sensationFor different stimuli – sensation is relativePerception is SUBJECTIVE, not absolute

SensationDefinition: stimulation of the sense organs

ThresholdsIntuitive definitionThe “threshold” of your house is your doorway. You’re outside until you pass through the threshold; then you are inside. This happens exactly at the door frame… every time… always the same…Do your eyes work like that?

Thought ExperimentYou have a two-mile long garage with no windows (pretend this isn’t ridiculous)

Thought ExperimentInside, you put a remote-controlled truck at one end. On top of the truck is an extremely tiny, faint light bulb. It has no other lights.

Thought ExperimentYou sit at the other end and turn off the lights. It’s pitch black.You hold the remote stick to start the truck moving toward you, slowly. Release the control to stop the truck as soon as you see the light bulb.TruckYou

Thought ExperimentTurn on the lights. Go to the truck and mark a chalk line on the floor where it stopped.Set up the truck again, turn off the lights. Start the truck. Stop it when you see the light. Mark the floor with chalk.Repeat this 100 times

Thought ExperimentIf your vision had a threshold like a doorway in a house, you would draw a chalk line in the same spot on the floor every time – 100 lines all on top of each other.That’s not what you get.

Thought ExperimentHere is what the chalk lines on the floor would look like, approximately:So where is the “threshold”?Note: this is a simplification. The lines wouldn’t be symmetrical as drawn above, but explaining why needs physics and math. The example is valid despite this simplification.

ThresholdsOperational definition of Threshold for lightThe minimum amount of light at which you detect it 50% of the time.In the thought experiment, it would be the point on the floor where 50% of the lines are in front of it, and 50% are beyond it.So about right here

If you graphed this, you would get the red curve.Note: the intuitive definition of a threshold is the blue curve

Truck getting closerThe horizontal axis is the distance of the truck from you.When the light on the truck is far away, it is a very low intensity.As the truck gets closer, the intensity of the light increases(This is physics. Google the Inverse Square Law if you’re curious why this happens.)

Think of the vertical axis as the percentage of the 100 chalk lines that the truck has crossed as it drives toward you.

NoneThink of the vertical axis as the percentage of the 100 chalk lines that the truck has crossed as it drives toward you.

CoupleThink of the vertical axis as the percentage of the 100 chalk lines that the truck has crossed as it drives toward you.

MoreThink of the vertical axis as the percentage of the 100 chalk lines that the truck has crossed as it drives toward you.

50%Think of the vertical axis as the percentage of the 100 chalk lines that the truck has crossed as it drives toward you.

MostThink of the vertical axis as the percentage of the 100 chalk lines that the truck has crossed as it drives toward you.

AllThink of the vertical axis as the percentage of the 100 chalk lines that the truck has crossed as it drives toward you.

Thresholds – Review and Main PointsYour eyes are not like cameras.There is variability in how you sense light.The intuitive idea of a “Threshold” simply does not fit.We use an operational definition of “absolute threshold” to describe how you really notice a stimulus.

Main Point 1. First PartThere is variability in sensation

Just Noticeable Differences (JNDs)Now that you see a light, how much does it have to change in intensity for you to notice it?This is the JNDThe size of the JND depends on how intense the first light is.

Just Noticeable Differences (JNDs)Example: You have a bulb that lets you go from 5 Watts to 10 Watts.You would see this difference.10 W5 W

Just Noticeable Differences (JNDs)But if you went from a 100 Watt bulb to a 105 Watt bulb, you would see no difference.A difference of 5 Watts is only noticeable if you start with dim bulbs.100 W105 W

Have you ever purchased a three-way bulb that goes from 50 Watts to 100 Watts to 150 Watts?You see a big change from dark to 50W, then a large increase in brightness when you click to 100W….but there’s only a tiny change after the third click to 150W.150 W100 W50 W

This is a similar idea to JNDs. The key point is that your eyes are not on an absolute scale. What you notice is relative to stimulus intensity!

Main Point 1. CompleteThere is variability in sensationFor different stimuli – sensation is relative

PerceptionDefinition: The selection, organization, and interpretation of sensory input

Playing with a truck in a fictional building was fun, but that isn’t the real world.The idea of an “absolute threshold” applies best to laboratories, or to silly situations like a two-mile long garage with no windows…In the real world, it is more complicated.

What if the survival of a plane full of people relies on you noticing this light as you look at this display

Signal Detection TheorySignal Detection Theory has direct applications in the design of many products.In the case of cockpits, it is essential.

Signal Detection TheoryWhether or not a pilot detects a warning light depends on:Stimulus Intensitythe idea of absolute threshold still appliesIf a light is too dim, the pilot doesn’t see itNoise in the environment“Noise” refers to stimuli competing for the same senseIn a cockpit, other lights, dials, flashes, and reflected lights are “noise”More noise  more intense warning light is needed for detectionYour Criterion for Deciding if you detect the stimulus

Signal Detection TheoryHere is where detecting a little warning light becomes a question of perception.You select, organize, and interpret sensory information. You matter.

Signal Detection TheoryGood situation:The pilot is vigilant, attentive, and motivated. He or she is concerned about doing the job well.Bad situation:The pilot feels comfortable flying, sees him or herself as a seasoned pro, and has the routine flight checklists so well learned that he or she can “do it in their sleep.”

Signal Detection TheoryGood situation:The pilot is vigilant, attentive, and motivated. He or she is concerned about doing the job well.This is a very sensitive criterionBad situation:The pilot feels comfortable flying, sees him or herself as a seasoned pro, and has the routine flight checklists so well learned that he or she can “do it in their sleep.”This is not a sensitive criterion

Main Point 2. Perception is SUBJECTIVE, not absolute.

Signal Detection TheoryReview – Detecting a stimulus depends on:Stimulus IntensityIf a light is too dim, the pilot doesn’t see itNoise in the environmentMore noise  more intense warning light is needed for detectionThe person’s criterion for deciding if they detect the stimulus

Four Possible OutcomesIn a signal detection situation, there are four possible outcomes as you try to detect the stimulus.Columns represent realityRows are the person’s decision.

Example: You order a pizza during a party. As you enjoy yourself, there is background noise. You are listening for the doorbell for the pizza person.

Right after placing the order, your Criterion is very low. You expect a “Correct Rejection,” where you don’t hear anything and nothing is at the door. This criterion increases risks of “Misses,” though. If they miraculously try to deliver a pizza 5 minutes after you call, you might not hear them ringing your doorbell!

However, 40 minutes later, your Criterion changes to high sensitivity. You want pizza! You want a “Hit,” but that also risks “False Alarms,” or thinking you hear a doorbell when there really was none.

What you expect, what you are doing, and how much you care about detecting the stimulus matters!Perception is subjective.

Main Point 2. Perception is SUBJECTIVE, not absolute.Different people can select, organize, and interpret the same stimulus differently.The same person can select, organize, or interpret the same stimulus differently on different occasions.

These ideas can be implemented and controlled in cockpit design, pilot training, and FAA regulations.Human Factors Engineering is an Applied field where Psychologists and other professionals use these ideas.Other situations do not have such extreme oversight, but lives are still at stake…

Example in NursingAlarm FatigueNurses constantly hear alarms going off during their jobs. Low battery alerts, I/V alerts, monitor alerts… The beeps, buzzes, and alarms each day can number in the 100s.The problem is that some of these are trivial and others are life threatening.

Example in NursingSituation: a nurse needs to hear a life threatening alarmSignal Detection TheoryThe loudness, pitch, and timbre of the alarm mattersThe “noise” in this case is all of the other beeps, blips, buzzes, and low priority alarms going offThe decision criterion is the nurse’s attentiveness and focus on the alarms

Example in NursingSituation: a nurse needs to hear a life threatening alarmPossible OutcomesHit– Nurse hears alarm, emergency response startedCorrect Rejection – Nurse hears no alarm, nothing is wrongFalse Alarm – Nurse “hears” alarm, emergency response started unnecessarily: wastes resources, time, and money. Is embarrassing…Miss– Nurse hears no alarm, a person suffers, or worse…

Example in NursingThe problem is that the diverse cacophony of alarms can lead to a criterion that looks like this:

Example in NursingGetting used to not reacting to alarms (Correct Rejections) leads to an increase risk of Misses.

Example in NursingUnfortunately, there are many manufacturers of equipment. Each hospital may have various models of equipment, all with different alarms. Different departments in the same hospitals have different systems…There is no equivalent to the airline manufacturer who designs everything in a cockpit to work together, with FAA oversight.Finding a solution needs applied research. Psychology is essential.

SummaryIn this slideshow, we used several topics from your text to introduce sensation and perception.Psychologists who study sensation and perception can be basic researchers or applied researchers.Sometimes basic research (spending years studying how people notice differences between sounds) can become essential for applied research.

SummaryYou read examples of Thresholds and Just Noticeable DifferencesFrom this, we illustrated the first main point:There is variability in sensation.For different stimuli, sensation is relative.Then you read a descriptions of examples of using Signal Detection TheoryFrom this, we illustrated the second main point:Perception is subjective, not absolute

Introduction to sensation and perception

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Introduction to sensation and perception