Intro to Psychology Practice Exam — Free

Work through each behaviour with the two questions that define any operant consequence: is a stimulus added or removed, and does the behaviour increase or decrease afterward?

The child. Behaviour: whining. Consequence: a cookie is added. Result: whining becomes more frequent. A stimulus is added and the behaviour increases, so the whining is positively reinforced.

The father. Behaviour: handing over a cookie. Consequence: the whining (an aversive stimulus) is removed. Result: he gives the cookie sooner each time, so the behaviour is strengthened. A stimulus is removed and the behaviour increases, so the cookie-giving is negatively reinforced.

Both behaviours increase, so neither is punished, which rules out option C. Option D is the most tempting mistake: the child is not escaping anything, a cookie is being added, so only the father's side involves removal. Option B swaps the two labels. The exchange is a classic reinforcement trap in which each person's behaviour maintains the other's.

Answer: A — the child's whining is positively reinforced and the father's cookie-giving is negatively reinforced.

The U-shaped curve is the serial position effect. Its two ends have different explanations in the multi-store model.

Primacy effect (early words). The first words arrive when short-term memory is empty, so each gets more rehearsal than later words. Rehearsal transfers them into long-term memory, which holds them through a delay.

Recency effect (last words). The final few words are recalled well in immediate recall only because they are still sitting in short-term memory, which has a small capacity and holds unrehearsed information for only a matter of seconds.

The 30-second counting task. Counting backward is a demanding, attention-filling task. It prevents rehearsal and displaces the last few words from short-term memory before the participant can report them. The early words, already in long-term memory, are unaffected. So the second group's curve keeps its high left end, but its right end drops to roughly the level of the middle items.

This is the pattern Glanzer and Cunitz reported in 1966: a filled delay before recall abolished the recency effect but left the primacy effect intact, which is strong evidence that the two effects come from separate memory stores.

Answer: the recency effect is eliminated and the primacy effect is preserved, because the distractor task clears short-term memory while the rehearsed early items are already in long-term memory.

Weber's law states that the just-noticeable difference is a constant proportion of the standard stimulus:

where $I$ is the standard intensity, $\Delta I$ the JND, and $k$ the Weber fraction for that sense.

(a) Weber fraction. Use the measured pair to find the constant: $k = \Delta I / I = 2\text{ g} / 100\text{ g} = 0.02$. The participant needs a 2% change in weight to notice a difference.

(b) JND at 1,500 g. Because the proportion is constant, scale it to the new standard: $\Delta I = k \times I = 0.02 \times 1{,}500\text{ g} = 30\text{ g}$. A heavier standard needs a larger absolute change, which is why a 2 g difference that is obvious at 100 g is invisible at 1,500 g.

(c) Testing 1,520 g. The difference offered is $1{,}520 - 1{,}500 = 20\text{ g}$, which is less than the 30 g JND, so the participant will not reliably tell the weights apart. The lightest comparison that reaches the threshold is $1{,}500 + 30 = 1{,}530\text{ g}$.

As a check, the same 2% rule applied to the original pair gives $k \times 100 = 0.02 \times 100 = 2$ g, matching the measured JND, and a 30 g difference at 1,500 g is again exactly 2%.

Answer: (a) $k = 0.02$; (b) JND = 30 g; (c) no, 20 g is below threshold; the comparison must be at least 1,530 g.