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Chapter 3: Sensation

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  • Ernst Weber

    The researcher/physiologist who conducted early studies on sensory thresholds and the detection of differences between stimuli.

  • Just Noticeable Difference (JND)

    The smallest detectable difference between two stimuli that a person can perceive 50% of the time. (Also known as the Difference Threshold).

  • Weber's Law

    The principle that two stimuli must differ by a constant minimum percentage (rather than a constant amount) to be perceived as different.

  • JND vs. Weber's Law

    JND is the specific amount of change needed to notice a difference in a given situation. Weber's Law is the rule stating this change is always a proportional percentage.

  • Absolute Threshold

    The minimum amount of stimulus energy needed to detect a particular stimulus 50% of the time. (Going from nothing to something).

  • Gustav Fechner

    The scientist who expanded on Weber's work and established the concept of the absolute threshold.

  • Absolute vs. Difference Threshold

    Absolute = detecting the presence of a stimulus. Difference (JND) = detecting a change in a stimulus.

  • Limen (Root word)

    Threshold (Think of it as the "doorway" or checkpoint to conscious awareness).

  • Supraliminal stimuli

    Stimuli that are above the absolute threshold. They are strong enough to be consciously detected. (Supra = above).

  • Subliminal stimuli

    Stimuli that are below the absolute threshold of conscious awareness. They are too weak or presented too quickly to be consciously perceived. (Sub = below).

  • What happens biologically when we are exposed to a subliminal stimulus?

    The stimulus is strong enough to physically activate our sensory receptors (like our eyes or ears), but the signal fails to reach conscious awareness in the brain.

  • Subliminal perception

    The process by which subliminal stimuli (signals outside of conscious awareness) act on the unconscious mind and subtly influence behavior or mood.

  • James Vicary

    A market researcher who famously claimed in 1957 that flashing subliminal messages ("Eat Popcorn") in a movie theater drastically increased sales. He later admitted the entire study was a hoax.

  • A market researcher who famously claimed in 1957 that flashing subliminal messages ("Eat Popcorn") in a movie theater drastically increased sales. He later admitted the entire study was a hoax.

    No. Decades of research show that while subliminal stimuli might cause a fleeting feeling, they cannot control behavior or force you to buy specific products.

  • Empirical Evidence

    Information gathered through real, observable, and measurable scientific studies—not just theories or claims. (This is what exposed Vicary's hoax).

  • Critical Thinking

    The practice of questioning extraordinary or "magical" claims and demanding scientific proof (empirical evidence) before accepting them as true.

  • Signal Detection Theory

    Signal detection theory is used to compare our judgments, or the decisions we make, under uncertain conditions. The ability to detect any physical stimulus is based on how strong it is and how mentally and physically prepared the individual is.

  • Signal Detection: Hit

    The stimulus is present, and you correctly detect it.

  • Signal Detection: Miss

    The stimulus is present, but you fail to detect it.

  • Signal Detection: False Alarm

    The stimulus is NOT present, but you incorrectly report that you detected it.

  • Signal Detection: Correct Rejection

    The stimulus is NOT present, and you correctly report that it is not there.

  • Habituation

    The brain's tendency to stop paying attention to constant, unchanging information. The sensory receptors are still firing, but the lower brain centers filter the signal out before it reaches conscious awareness.

  • Sensory Adaptation

    A decrease in the physical responsiveness of sensory receptor cells to an unchanging stimulus. The receptors themselves physically stop sending the signal to the brain

  • A decrease in the physical responsiveness of sensory receptor cells to an unchanging stimulus. The receptors themselves physically stop sending the signal to the brain

    Habituation happens in the brain (filtering), while sensory adaptation happens at the receptor level (cells stop responding).

  • Why doesn't our vision fade from sensory adaptation when we stare at something?

    Because of microsaccades. These tiny, involuntary eye vibrations constantly shift the image to fresh receptor cells, preventing them from adapting.

  • Microsaccades

    Constant, tiny, involuntary vibrations of the eye that prevent sensory adaptation to visual stimuli.

  • Saccades

    Rapid, voluntary or reflexive jumps of the eye from one point of focus to another (such as the jumping movements the eye makes while reading).

  • Light has properties of both

    waves and particles

  • who first proposed that light is actually tiny “packets” of waves

    Albert Einstein, who first proposed that light is actually tiny “packets” of waves

  • what is other name of wave particles

    Photons

  • Three aspects of perception of light

    Brightness, color and saturation

  • how brightness is determined

    Brightness is determined by the amplitude of the wave—how high or how low the wave actually is.

  • Higher the wave

    he brighter the light appears to be

  • Lower the wave

    dimmer the light

  • How color or hue is determined

    he brighter the light appears to be: short wave or long wave

  • which side of the spectrum short waves found at

    Blue

  • which side of the spectrum long waves found at

    Red

  • what is saturation

    Saturation refers to the purity of the color people perceive:

  • A highly saturated red would contain only

    Red wavelength

  • less saturated red would contain

    mixture of wavelengths