Tom Foulsham¹ (foulsham@essex.ac.uk), Arnold Wilkins¹; ¹University of Essex

The widespread use of LED lighting, which can flicker at a high rate, has raised questions about the effects of this temporal light modulation (TLM) on visual tasks such as reading. In particular, TLM has been linked to visual discomfort and may disrupt eye movements. This may be because during a saccade the TLM can generate a spatial pattern known as a “phantom array”. This may interact and interfere with the pattern formed by the letter strokes. We measured reading speed and eye movements in two tasks. In the first task, participants read aloud monosyllabic, high-frequency words presented in a random order as a paragraph. In the second task, participants read meaningful paragraphs, silently, before answering a series of comprehension questions. In both tasks the text was presented on paper and illuminated by LEDs with TLM at 120 Hz, 600 Hz or 60 kHz. Illumination was modulated as a square wave, with a duty cycle of 30%, conditions in which the phantom array is maximally visible. Participants showed slower reading speeds with text containing words with high horizontal autocorrelation. There were also small effects of TLM, with slower reading in both tasks at 600 Hz, where the phantom array is easily visible. We discuss further nuanced effects of TLM on fixation duration and position, as well as interactions with individual differences in visual sensitivity. We conclude that striped text and TLM both slow reading, perhaps due to disrupted eye movements.