Supporting People with Acquired Brain Injury to Use a Reminding App; Narrow-deep vs. Broad-shallow User Interfaces
Matthew Jamieson, Marilyn Lennon, Breda Cullen, Stephen Brewster, Jonathan Evans · 2022 · ACM Transactions on Accessible Computing · doi:10.1145/3501275
Summary
This study compares two contrasting user interface approaches for smartphone reminder apps used by people with acquired brain injury (ABI). "Broad-shallow" interfaces show lots of information on fewer screens (requiring scrolling), while "narrow-deep" interfaces present one piece of information per screen across many screens. Most commercial reminder apps, including Google Calendar, use broad-shallow design—but this may not be optimal for users with cognitive impairments. The researchers developed ApplTree, a reminder app that can toggle between both UI types, and tested it with 32 participants with ABI (mean age 49, median 4 years post-injury). Participants set six reminders using both interfaces in a counterbalanced design, while researchers measured accuracy, speed, guidance requested, and task load (NASA-TLX). Participants also completed neuropsychological assessments measuring memory (Rivermead Behavioural Memory Test), executive functioning, and selective attention (Delis-Kaplan Executive Function System). The study addresses a significant real-world gap: while 79% of people with ABI use paper calendars, only 38% use smartphone reminders despite owning phones. The researchers hypothesized this adoption gap is partly due to usability barriers in current app designs that don't account for cognitive impairments affecting attention, memory, and executive function.
Key findings
Participants made significantly more errors using broad-shallow UI: 2.96 mistakes per reminder versus 2.29 with narrow-deep (p=0.002). For every three reminders set, people made approximately two additional errors with broad-shallow. Critically, this difference was driven by omissions—participants simply missed entering required information (147 omissions in broad-shallow vs 78 in narrow-deep). Fields most commonly omitted included notes, loudness settings, and notification times. There were no significant differences in speed (narrow-deep averaged 278 seconds vs 257 for broad-shallow), guidance requested, or perceived task load between interfaces. This is important: narrow-deep improved accuracy without making the task slower or more demanding. Participant preference was split: 12 preferred narrow-deep, 10 preferred broad-shallow, and 4 had no preference. Those favoring narrow-deep cited handling "one thing at a time," missing less information, and preferring button presses to scrolling. Those favoring broad-shallow valued the ability to review all information at once and feeling less likely to lose track of their progress. An unexpected finding: participants with better selective attention and more smartphone experience benefited most from narrow-deep—the opposite of what researchers predicted. This suggests narrow-deep may help experienced users attend to details they would otherwise rush past.
Relevance
This research directly challenges mainstream app design conventions. Nearly all commercial reminder apps use broad-shallow interfaces, yet this study demonstrates that design choice leads to significantly more errors for people with cognitive impairments. For the 387 million people projected to have neurological impairments by 2030, this has real consequences: a missed medication reminder or forgotten appointment due to an omission error. For developers, the findings support WCAG 2.1 guideline 1.3 ("Creating content that can be displayed in different ways without losing information or structure"). Apps could offer users the choice between UI styles, or default to narrow-deep for first-time users before transitioning to broad-shallow as proficiency develops. The study also highlights the value of "micro-prompting"—breaking complex tasks into individual steps presented one at a time. This wizard-style approach, familiar from software installation, may be broadly beneficial for cognitive accessibility. However, the split preferences underscore that one size doesn't fit all: some users genuinely work better with everything visible at once. Configurable interfaces that respect user agency while defaulting to more accessible options represent a practical path forward.
Tags: acquired brain injury · cognitive accessibility · user interface design · assistive technology · memory aids · prospective memory · mobile apps
Standards referenced: WCAG 2.1