Effects of Aging on Small Target Selection with Touch Input
Afroza Sultana, Karyn Moffatt · 2019 · ACM Transactions on Accessible Computing · doi:10.1145/3300178
Summary
This study provides a detailed analysis of age-related touch selection errors on small touchscreen devices, extending prior work on mouse and pen interaction to finger touch input. Twenty older adults (ages 67-81, M=73.3) and sixteen younger adults (ages 22-35, M=28.9) completed a two-dimensional Fitts task on an Android smartphone, selecting circular targets at three sizes (4.88mm, 7.22mm, 9.22mm) across eight movement directions and two amplitudes. The researchers measured movement time, error rate, finger pressure, endpoint variability, and categorized selection errors into miss errors (landing and lifting outside the target) and slip errors (landing on target but slipping outside before lifting). Beyond basic performance metrics, the study provides fine-grained analysis of error types and their subcategories, offering insight into the specific difficulties older adults encounter with touch input that differs from both mouse and pen interaction.
Key findings
Older adults were significantly slower (947ms vs 713ms) and made more errors (32.17% vs 9.17%) than younger adults, with error rates disproportionately increasing as target size decreased—for the smallest targets (4.88mm), older adults had 62.4% error rates versus 24.9% for younger adults. Critically, miss errors dominated over slip errors for touch input (older adults: 27.87% miss vs 4.29% slip), contrasting with pen interaction where slips dominate. This suggests touch and pen require different accessibility solutions despite both being "direct" input. Aging influenced both miss and slip errors for touch, whereas for pen interaction age only affects slip errors. Older adults showed greater endpoint variability (mean distance from target center: 3.36mm vs 1.92mm for younger adults), higher finger pressure, and a tendency to overshoot targets in the lower-right quadrant due to hand occlusion. Error recovery was also more difficult: while younger adults corrected errors within 12 attempts, 7% of older adult error trials required more than 12 corrective attempts. Near-miss errors (within 50% of target radius) accounted for 64% of older adult miss errors, indicating small adjustments could prevent many failures.
Relevance
This research provides concrete guidance for accessible touchscreen design. The finding that errors significantly decreased at 9.22mm and larger suggests a minimum target size of approximately 9-10mm for older adult accessibility—consistent with current platform guidelines but often violated in practice (smartphone icons can be as small as 4mm). The dominance of miss errors over slip errors for touch indicates that accessibility techniques developed for pen input (which target slip reduction) may not transfer directly; techniques reducing miss errors—such as area cursors, target expansion, bubble cursors, and zooming—warrant exploration for touch. The observation that many errors were near-misses suggests "snap-to-target" or expanded activation areas could substantially improve accuracy. Finally, the finding that older adults applied more finger pressure and had larger finger contact areas explains some endpoint variability and suggests that touch registration algorithms accounting for larger, variable contact patches could improve selection accuracy for older users.
Tags: older adults · aging · touchscreen · mobile accessibility · target selection · Fitts Law · motor control · error analysis