Prompts need a minimum interval between them
Aliases: blink dip · notification pacing design
What it is
Given the attentional blink's time window, the safe interval to leave between consecutive prompts is neither "as short as possible" nor "as long as possible" — it needs to skip over the roughly two-to-five-hundred-millisecond range where the blink is deepest. An interval that happens to land right in that range is actually a worse choice than one that is either a bit shorter or a bit longer.
Why it happens
The blink effect traces a U-shaped curve as a function of interval: at extremely short gaps (tens of milliseconds), lag-1 sparing kicks in and the two prompts are often processed as a single event, giving a relatively high detection rate; as the gap stretches to around two to three hundred milliseconds, detection rate drops to its lowest point; once the gap extends past half a second, the first prompt's consolidation is already complete and detection rate returns to baseline. This non-monotonic shape means that simply "adding some delay" between consecutive prompts is not automatically an improvement — if the added delay lands right in the dip, it performs worse than no delay at all.
Studying it
This conclusion draws on the lag-vs-accuracy curve measured with the RSVP paradigm; the exact location of the dip and the recovery point vary somewhat with task difficulty and target discriminability. Interface design should not copy a precise millisecond figure from a single paper — instead, treat the curve's shape (U-shaped, with a genuine dip) as a design constraint, and determine the real dip location for a given notification scenario through direct measurement in the actual product, since presentation format (a continuous visual character stream vs. an interface popup notification) carries different processing load and will shift where the dip falls.
Where it stops holding
- This conclusion assumes users must consciously identify each prompt. If a prompt is purely ambient (no specific content needs to be reported — a background color change signaling status, say), the blink effect does not apply and interval design is not bound by this constraint.
- The exact dip range is heavily influenced by presentation format; classic lab figures (measured with a continuous visual character stream) should not be used directly as a product's interval parameter — they must be re-measured for the actual prompt format in use.
- A user's specialized training can narrow the width of the dip slightly, but does not eliminate it.
Applying it
- Avoid designing consecutive prompts to appear as "the moment one is handled, present the next" — a near-zero gap tends to land at the start of the dip rather than genuinely benefiting from lag-1 sparing's higher detection rate.
- Avoid setting a fixed delay that "looks short enough but is actually arbitrary" (two to three hundred milliseconds, say) — that range is exactly the bottom of the blink curve, the worst possible choice.
- If a product genuinely needs rapid consecutive prompts, favor one of two boundary strategies: an interval short enough (tens of milliseconds) that adjacent prompts are treated as one event — but this only works when the two prompts' content can genuinely be understood together — or an interval long enough (half a second or more) that the first prompt fully consolidates before the next appears. The middle ground is the range to actively avoid.
- Verification: for the specific prompt format and pacing in use, measure the second prompt's detection rate across a range of intervals, plot the real dip for this product context, and set the interval based on that measurement rather than a millisecond figure borrowed from a paper.