sensory systems midterm 1

Perceptual Illusion

Perceptual Illusion

A discrepancy between what is perceived and what is physically present in the real world.

Optical Illusion

A discrepancy between what is in the retinal image and what is present in the real world.

Sensation

The ability to detect a stimulus, and perhaps to turn that detection into a private experience.

Perception

Giving meaning to a detected sensation.

Steps in the sensory process

Physical stimulus → physiological response → sensory experience.

Physical Stimulus→ Physiological Response (Techniques)

Animal single-unit recording and human brain imaging (MEG, PET, FMRI, & ERPS).

Physiological Response → Sensory Experience (Techniques)

Animal lesion studies, human clinical studies, human brain imaging.

Physical Stimulus → Sensory Experience (Techniques)

Behavioural techniques.

Newton’s Study of the Sensation Process

The assigned colour names to different wavelengths of light, which created the spectrum of visible light.

Newton’s Study of the Sensation Process (problems)

It was qualitative and there was no assurance that all humans had the same sensory experience.

Fechner

Invented psychophysics and is known as the true founder of experimental psychology.

Psychophysics

The science of defining quantitative relationships between physical and psychological (subjective) events.

Absolute Threshold

The minimum amount of stimulation necessary for a person to detect a stimulus 50% of the time.

Psychometric Function

A graph of stimulus value (ex. intensity) on the horizontal axis versus the subject’s responses (ex. proportion yes) on the vertical axis.

Ogive

The typical S shape of real psychometric functions.

Relationship between Absolute Threshold and Sensitivity

The lower the absolute threshold, the higher the persons sensitivity.

Method of Constant Stimuli (detection)

Select stimulus intensities above and below the expected threshold → present many trials of each intensity in random order → plot psychometric function → read o.5 (50%) detected point from graph.

Method of Limits (detection)

Alternate between ascending (intensity increase until response = yes) and descending (intensity decrease until response = no) series with varying start points → calculate a crossover point for each series → find the average of all crossover points.

Method of Adjustment (detection)

Experimenter randomly adjusts starting point (usually position of potentiometer) → observer adjusts stimulus intension, using a potentiometer, until it is just detectable (many times) → calculate average of these threshold adjustments.

Suprathreshold Stimulus

A stimulus that is always above the absolute threshold, and is therefore always detectable.

Difference Threshold

The smallest difference between stimuli or change in a stimulus that the observer notices 50% of the time (also called a just noticeable difference [JND])

Method of Constant Stimuli (discrimination)

A standard and comparison stimuli are presented together and the magnitude of comparison (above and below standard) is varied in random order with many trails → plot proportion “bigger” responses versus comparison magnitude (0.75 is upper limit, 0.25 is lower limit)

Just Noticeable Difference Formula

(upper limit - lower limit)/2

Point of Subjective Equality

The 0.5 point on a discrimination graph [(upper limit + lower limit)/2]. Used as a measure of accuracy.

Method of Limits (discrimination)

Standard and comparison stimuli presented together. Descending and ascending series presented in equal spets till response changes from stronger/weaker to equal to stronger/weaker. Upper limit is crossover point between stronger and equal on each series and lower limit is crossover point between equal and weaker on each series.