Here are two tasks. Both take a few seconds. Both would be described by anyone watching as easy.
In the first, a photograph of a dog appears at the top of the screen. Below it, two photographs: the same dog, and a chair. The child touches the dog.
In the second, the tablet says the word “dog”. Below, the same two photographs. The child touches the dog.
Same child, same afternoon, same two pictures, both at 95%. In an earlier article we argued that repetition is not relation — that a child can score highly on a matching task without comparing anything. Both of these tasks sit on that side of the line: both are what Emilio Ribes calls coupling, recognising and repeating. Neither requires comparing.
So by the structure of the task they are the same thing. And yet anyone who has sat with a child through both knows perfectly well that they are not. This article is about what the difference actually is, because naming it changes what you do next.
What makes them the same
Ribes’ criterion is structural, and it is strict. A contact is coupling when the contingencies of occurrence stay constant — when nothing permutes from trial to trial. In both of our tasks, the dog photograph is always the right answer for the dog. Nothing swaps roles. There is no rule in force that could change and make the same object wrong on the next trial.
That is the honest reading, and it is why both tasks land in the same box.
What makes them worlds apart
Ask a different question: what holds the correspondence together?
In the identity task, the answer is right there on the screen. The photograph at the top and the photograph below it share their form — the technical word is isomorphism. Everything the child needs in order to be right is present in the field, here and now. What the task asks of them is to tell apart the perceptual features that make up that sameness, which is exactly the adjustment criterion Ribes assigns to this contact: differentiality.
In the word→picture task, nothing of the sort is available. There is nothing dog-shaped about the sound “dog”. The two are not similar, not analogous, not connected by any property either of them has. What holds them together is convention — an agreement made by a community of speakers long before this child was born — and reaching it requires a conventional medium of contact in the first place.
One correspondence is held up by what is present. The other is held up by nothing that is present at all.
Two axes, not one ladder
The usual way to read Ribes is as a single ladder: contacts get more complex as you climb, each one demanding more than the last. Read that way, our two tasks are at the same rung, and the difference above simply disappears.
We find it more useful to read it as two independent axes.
Recursion — how much has to be held at once. How many things must be kept in play for a response to be correct: one datum, a rule, a rule that depends on another rule. On this axis our two tasks genuinely are at the same point. Simple pairings, nothing permuting, nothing to keep in suspension.
Anchoring — who holds the correspondence. At one end, what is present: the field itself supplies the reason the answer is right. At the other, convention: the reason lives entirely outside the situation, in a shared agreement, and has to be carried into it. On this axis our two tasks are at opposite extremes.
Two tasks, identical on one axis, as far apart as they get on the other. That is why the single ladder cannot see the difference, and why we keep the second axis.
A distinction worth not blurring
It is tempting to say the word and the photograph “differ in dimension”. They do not, and the sloppiness costs something later.
A dimension is the respect in which things are being compared — colour, size, taste. It is the in what way. A word and a photograph of a dog are not two values of one dimension; they are the same content arriving through a different channel and in a different format. Different axes of the model entirely. Keeping them apart is what makes it possible to say precisely what a probe is testing.
The part that matters at the table
Here is the consequence, and it is the reason any of this is worth an article.
The same word→picture task can be two completely different contacts, depending on the child’s history.
If “dog” is functioning for the child as an acoustic pattern — a particular noise, in a particular voice, that has come to be followed by touching a particular picture — then the task is pure coupling. Recognise a sound, repeat a gesture. Nothing about it is language.
If “dog” is functioning as a word, something else is going on entirely.
The task on screen is identical in both cases. The child’s accuracy is identical. And the score cannot separate them — which is the same lesson as the first article, arriving from a new direction: performance tells you how often the child was right, never what made them right.
How you would actually tell
Only one thing distinguishes them, and it is not a harder version of the same task. It is a probe: change something the acoustic pattern depends on but the word does not, and see whether the answer survives.
If “dog” is working as a word, it should survive:
- another exemplar — a different dog, one the child has not seen;
- another voice — the same word said by someone else;
- the written word — the same content through a different channel again.
If it is working as an acoustic pattern, the first may survive and the other two will not.
We should be straight about which of these Interlaza can run today. The exemplar probe is implemented: the early stages close by redrawing the answer in its other variant, realistic photograph to pictogram, with no feedback and no bearing on progression. The other-voice and written-word probes are not. They are not blocked by anything conceptual — the library simply holds one recording per concept per language, so a different-voice probe needs recordings made, not code written. We would rather say that plainly than let the shape of the argument imply a feature that does not exist.
What to do with this
Mostly, stop letting “simple” do so much work.
Two stages that both look easy, that both sit early in a route, that a child passes at the same rate, can be resting on completely different foundations. One is asking them to see a sameness that is in front of them. The other is asking them to bring something to the situation that is not in it at all — and a child who does that has done something considerably more interesting than the accuracy suggests.
Which returns to where the first article ended. The criterion is never in the cards. Somebody holds it — the instructor, the family, the community that agreed what each word names. What this second axis adds is that how far away that somebody is standing is itself part of what makes a task hard, and it is not visible in any score.
Interlaza draws on the interbehavioural tradition (Kantor; Ribes and López), Varela and Quintana’s Competence Transfer Matrix (1995), Sidman’s stimulus equivalence, and Relational Frame Theory. Full references are on our science page.