Classroom demonstration

The Stimulus Suffix Effect

Neath, I., Surprenant, A. M., & Crowder, R. G. (1993). The context-dependent stimulus suffix effect. Journal of Experimental Psychology: Learning, Memory, and Cognition, 19(3), 698–703. https://doi.org/10.1037/0278-7393.19.3.698

This demo shows the basic stimulus suffix effect. You hear a list of nine digits and then recall them in order. Each list ends with a signal you can ignore: either a tone or a spoken “baa.”

Run lists

Turn your sound on or use headphones. Half the lists end in a tone and half end in a spoken “baa,” in random order. After the list ends, click the digits in the order you heard them. Use Skip for a position you can’t remember. You can also type the digits, use 0 to skip, Backspace to undo, and Enter to finish.

Number of lists

READY

Press Start to begin.

One digit starts every second; the suffix starts one second after the ninth digit.

What the demo shows

When lists are heard, recall of the last item is usually very good. A spoken item added after the list (a suffix) sharply reduces recall of that last item, even though it carries no information and you know it is coming. A tone at the end of the list does not.

Your data from this session

Your lists stay in this page only. Nothing is saved; reloading or closing the page erases them. A digit counts as correct only if you put it in the position where it was presented.

All lists

How this demo differs from Neath et al.’s experiments

The classic explanation is a precategorical acoustic store: a brief, raw auditory memory that keeps the sound of the last item available, until a later speech sound overwrites it. Because the store was thought to hold sound before it is interpreted, only the acoustic properties of the suffix should matter. Neath, Surprenant, and Crowder (1993) tested that assumption. They played everyone the same recorded “baa,” spoken by the voice that read the lists. When listeners were told a person said it, it reduced recall of the last item; when they were told it came from a real sheep, it did not. How listeners interpreted the sound changed the suffix effect, which a purely precategorical store cannot explain. This demo uses only the speech version of “baa” and a tone, so it shows the effect their study built on, not their labeling manipulation.

The demo shows only the basic suffix effect. Neath et al. compared groups told that the same “baa” came from a person or from a sheep, alongside real cow and dog recordings or a person saying “moo” and “woof.” Here “baa” is always speech, and the comparison is with a tone.
In their Experiment 1, lists ending in a 1000-Hz tone were practice lists given at the start of the session. Here the tone lists are mixed at random with the speech lists, as a nonspeech comparison.
Their lists and suffixes were recordings of one British male speaker, each item in a 500-ms sound envelope with 500 ms between items, and their “baa” was that person imitating a sheep. Here the digits and “baa” are recordings of a synthesized British male voice (Apple’s “Daniel”), 330–600 ms long, with one starting every second. As in their study, the suffix is in the same voice as the list.
The demo uses digits 1–9 in random order, as in their Experiment 2. Responding by clicking digits in order follows their Experiment 1, which used on-screen letter buttons. The Skip button is an addition.
Their participants heard 45 lists (Experiment 1) or 60 lists (Experiment 2). With only a few lists, each point in your graph rests on a handful of right-or-wrong answers, so expect jagged curves.