Sensory factors limiting horizontal and vertical visual span for letter recognition

Area of Science:

• Visual perception
• Reading science
• Human-computer interaction

Background:

• Reading speed differs between horizontal and vertical English text.
• Slower vertical text reading is linked to a reduced visual span (Yu et al., 2010).
• Potential factors influencing visual span include resolution, mislocations, and crowding.

Purpose of the Study:

• Identify the primary determinant of visual span size.
• Explain the horizontal-vertical difference in reading speed.
• Investigate factors limiting visual span above critical print size.

Main Methods:

• Decomposition analysis to quantify information loss in letter recognition.
• Measured contributions of resolution, mislocations, and crowding.
• Compared information loss across horizontal and vertical text conditions.

Main Results:

• Crowding accounted for 75% of information loss in visual span.
• Mislocations contributed 19% to information loss.
• Resolution (declining acuity) accounted for only 6% of information loss.

Conclusions:

• Crowding is the dominant factor limiting visual span size.
• Stronger crowding along the vertical midline explains slower vertical text reading.
• Understanding crowding is key to optimizing text display for reading.