חוש, תפיסה ופסיכופיזיקה
הוצג| English | משמעות |
|---|---|
| difference threshold/ˈdɪfrəns ˈθreʃəʊld/ | סף הבדל |
| transduction/trænsˈdʌkʃn/ | המרה |
A decision before an answer
- A just-noticeable difference is not a fixed amount of stimulus; it is a fixed fraction.
- Your goal: Distinguish thresholds, Weber's law and signal-detection measures.
Measure the thresholds
- Psychophysics relates physical intensity to experience. An absolute threshold is a stimulus level meeting a specified detection criterion under specified conditions, often 50% detection; a difference threshold is a detectable change under a stated criterion.
- Weber's law states that the difference threshold is a constant fraction of the baseline: ΔI/I=k. With k=.02, a 100 g weight needs a 2 g change, while 200 g needs 4 g. Fechner proposed that perceived intensity grows logarithmically with physical intensity.
With Weber fraction k=.02, the just noticeable difference for a 250 g baseline is:
Difficulty 1/5 · 100 coins + a small bonus on first completion today
ΔI=k×I=.02×250=5 g.
Separate sensitivity from bias
- Real detection is noisy, so signal detection theory separates sensitivity from bias. Presenting signal or noise on each trial gives four outcomes: hits, misses, false alarms and correct rejections.
- Sensitivity d′ measures how separated the signal and noise distributions are; the criterion measures the observer's willingness to say yes. A payoff change can move the criterion without changing d′, so hit rate alone is not sensitivity.
After a payoff change, an observer says yes more often while the stimulus is unchanged. In signal detection theory, what moved?
Difficulty 1/5 · 100 coins + a small bonus on first completion today
Payoffs move the criterion (bias); sensitivity depends on the signal and noise distributions.
Convert energy to signals
- Sensation begins with transduction: receptors convert physical energy into neural signals, as photoreceptors convert light and hair cells convert sound pressure.
- Sensory adaptation reduces response to a constant stimulus. Dark adaptation is the recovering sensitivity of the visual system in low light.
With Weber fraction .02, detecting a change from 50 g needs 1 g, and from 500 g needs 10 g. A radiologist who says yes more often after a pay-per-hit scheme shifts criterion, not d′. A listener who cannot distinguish two within-category speech sounds shows categorical perception of a physically continuous dimension.
Weber's law states that the difference threshold equals k times the ____.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
ΔI/I=k: the just noticeable change scales with the starting intensity.
Organise the percept
- Perception organises input rather than copying it. Gestalt principles group by proximity, similarity, closure and good continuation.
- Bottom-up processing builds percepts from features; top-down processing applies context and expectation. Categorical perception treats continuous acoustic variation as discrete phonemes: within a category, differences are hard to hear even when physically present.
Treating the difference threshold as a fixed amount rather than a fraction of the baseline, or reading a higher hit rate as better sensitivity when the observer simply says yes more.
איזו תשובה מתאימה למקרה זה?
הבחנה בין סף תפיסה, חוק ובר ומידות זיהוי אות
A higher hit rate by itself demonstrates higher sensitivity.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
Hits rise when the criterion loosens, even with unchanged d′; sensitivity and bias are separate.
Keep the distinctions
- difference threshold 差别阈限 — The minimum detectable change in a stimulus, a constant fraction of the baseline by Weber's law.
- transduction 换能 — Conversion of physical stimulus energy into neural signals by receptors.
- Distinguish thresholds, Weber's law and signal-detection measures.
- Trace transduction from physical stimulus to neural signal.
- Apply perceptual organisation and categorical perception principles.
Match each term with its precise meaning in this lesson.
Difficulty 2/5 · 140 coins + a small bonus on first completion today
Keep the distinctions stated in the teaching example.
Put this lesson’s reasoning or event sequence in order.
Difficulty 3/5 · 200 coins + a small bonus on first completion today
The order follows the stated process; check each stage before the next.