Table 1.

Summary of results from previous studies of foveal crowding.

Study	Maximal spatial extent of crowding: critical spacing (CS)	Maximal crowding	Target stimulus and task	Target size	Flankers	Dur-ation (ms)	Notes
Flom et al. 1963	~1.9–3.2′ E-E	0.9–1.3′	Landolt C	2.5′–3.3′	bars	∞	Viewing distance set to yield ~80% unflanked.
Danilova and Bondarko 2006 (Experiment 1)	1.5–4′ E-E	1–2′	Landolt C	2.1–4.7′	bars	500	Viewing distance: 1.7–8.1 m. Critical spacing for asymptotic performance estimated by eye from their Fig. 2.
Danilova and Bondarko 2006 (Experiment 3)	2.5–5′ E-E	0′	Tumbling E	3.5′ and 4.4′	Tumbling Es	500	Viewing distance: 1.7–8.1 m. Critical spacing for asymptotic performance estimated by eye from their Fig. 6.
Strasburger 1991	X	X	Numbers	3.6′	Numbers	100	3.6′ (0.06 deg) was the smallest size tested, with flankers 7.2′ center-center distance. No effect of flankers on threshold contrast.
Wolford and Chambers 1984 (foveal condition)	>6′ E-E	2.4′ (2 of 4 subs.)	Square with gap	12′	lines	17–33	Short duration adjusted to reduce performance.
Siderov, Waugh, Bedell 2013	4′ E-E	1′	Sloan Letters	~4′	bars	∞	high-contrast condition
Toet & Levi 1992	3.6′ C-C	—	T orientation	~1.8–4′	Ts	150	CS: spacing with 75% correct. Target size estimated as (1.2–2.6′) *1.5
Lev et al. 2014	>2.8′ E-E	—	E (left or right)	7.2′	E	30–250	Extent not measured, but crowding found at 0.4 character widths
Pelli et al. 2016	3.9′ C-C	—	10 numbers, novel font	1.2′ (width)	numbers	∞	Novel font with tall, thin letters. 2–10 m distance.
Present results	0.75–1.3′ E-E	0.5′	Tumbling E	1.85′–4′	Tumbling Es	∞	Conditions for 80–95% performance.