Simon task: the position you were told to ignore

The original demonstration in 1967 had nothing on a screen. Participants heard the word “left” or “right” arriving in one ear or the other and were told to respond to the word, with the ear it came through carrying no information at all — and responses were slower when the ear disagreed with the word. Everything since, including the version on this page, is an adaptation of that idea to a stimulus sitting off to one side of a display, which is why a page presenting two squares on a screen owes its readers a note that this is the visual variant. The span of costs reported in the literature is 20-60 ms, per Simon & Rudell (1967), Auditory S-R compatibility: The effect of an irrelevant cue on information processing, Journal of Applied Psychology, and it is noticeably smaller than the figures quoted for color-word conflict — a fact that gets read as the two tasks being the same phenomenon at different strengths, which is the mistake this page exists partly to correct.

The useful way to tell conflict paradigms apart is to ask which pair of things actually overlaps. In a color-word task the ignored property is a feature of the object being identified and it competes at identification: the word and the ink are two answers to the question “what color is this,” and the wrong one arrives first because reading is more practiced than naming. Here the ignored property is not an answer to the question at all. It is not a shape, it does not appear in the instructions, and no key on the keyboard is labeled with a position. What it overlaps is the response set — the fact that one key is operated by the left hand and the other by the right — and that overlap is created by the answering arrangement rather than by the display. Kornblum, Hasbroucq and Osman (1990), Dimensional overlap: cognitive basis for stimulus-response compatibility — a model and taxonomy, Psychological Review, sorts conflict tasks by exactly this question and puts the two in different families.

The evidence that the split is more than bookkeeping is in the distributions, and it is the reason this page bins your own trials instead of reporting one average. Sort a person’s correct responses from fastest to slowest and recompute the cost within each slice, and the two paradigms move in opposite directions: the correspondence cost is at its largest among the fast responses and fades among the slow ones, while a color-word cost grows as responses lengthen. Pratte, Rouder, Morey and Feng (2010), Exploring the differences in distributional properties between Stroop and Simon effects using delta plots, Attention, Perception & Psychophysics, puts the two side by side. Two effects generated by one mechanism could not have opposite shapes, and a page that averages either of them into a single millisecond figure has thrown that away. Twenty trials to a bin is far too thin to make a claim about one person, which the result panel says where it says it — but the shape is visible often enough to be worth showing, and it is the reason to run the Stroop test on the same machine and compare. A third arrangement, where the distraction is neither part of the object nor part of the response but simply sits next to the target, is the flanker task. Conflict of a slower and more deliberate kind — a rule that changes without warning — is the Wisconsin card sorting test, speeded symbol matching with no conflict in it at all is the digit symbol substitution test, and the classic pen-and-paper switching task is the trail making test.

A reaction time here is the interval between the frame that painted the stimulus and the timestamp the browser attached to your key, both read from the same monotonic clock. What neither can see is the display pipeline behind it, so on a 60 Hz screen roughly 16 ms of every figure below is the machine rather than you. That is the timing floor: two numbers closer together than that are the same number, and this page reports no precision it cannot support.

This is a measurement exercise, not a clinical assessment. It reports what you did on this page against a stated reference and nothing more — it cannot establish an attention condition, an impulse-control problem or a motor disorder. Only a qualified professional, working with more than a browser, can make that judgment.