Pelli Lab


The uncrowded-span model of reading rate — Pelli et al. (2007) describe a model of reading rate. Levi et al. (2007) apply it to reading by amblyopes. Here we provide a MATLAB program that fits the model to human data (e.g. Chung et al., 1998) and plots a figure. The program is pure MATLAB, compatible with MATLAB 7 on any computer. (Tested only under Mac OS X.) [Download]
  • Chung, S. T. L., Mansfield, J. S., Legge, G. E. (1998). Psychophysics of reading. XVIII. The effect of print size on reading speed in normal peripheral vision. Vision Research, 38, 2949–2962.
  • Levi, D. M., Song, S., & Pelli, D. G. (2007) Amblyopic reading is crowded. Journal of Vision, 7(2):21, 1-17,
  • Pelli, D. G., Tillman, K. A., Freeman, J., Su, M., Berger, T. D., & Majaj, N. J. (2007) Crowding and eccentricity determine reading rate. Journal of Vision, 7(2):20, 1-36,
Drifting grating movie. 
Psychophysics Toolbox — A free software package for vision research. Its routines provide an efficient interface between a high-level interpreted language (Matlab) and the display hardware on Macintosh and Windows computers. It also provides interfaces for timing, sound, and keyboard. The number of Psychtoolbox installations (with unique internet addresses) was 4,598 in December 2007. (See the overview for the current count.) Of these, 1634 are running under Mac OSX, 2958 under Windows and 6 under Linux. (We estimate that a further several hundred computers are still running the Mac OS 9 version of the Psychtoolbox.) The Psychtoolbox forum averages more than 3 messages a day. We know of 126 grant-supported projects that use it. And 404 papers cite it. (With David Brainard, Allen Ingling, and Mario Kleiner.)

Quest — A free software package for threshold estimation. It will run on any computer with MATLAB 5 or better. It is distributed both on its own and as part of the Psychophysics Toolbox (above). It's easy to use, has a sound theoretical footing, and is robust. We use it for all our work and recommend it without reservation. It's quite popular. You can download it as a stuffit or zip archive.

pdf  Watson, A. B. & Pelli, D. G. (1983) QUEST: a Bayesian adaptive psychometric method. Percept Psychophys, 33 (2), 113-20.  297 cites  

VideoToolbox — A free collection of two hundred C subroutines for Macintosh computers to calibrate and control the computer-display interface, making it possible to create accurately specified visual stimuli. This became the foundation for the Psychophysics Toolbox.

pdf  Pelli, D. G. (1997) The VideoToolbox software for visual psychophysics: transforming numbers into movies. Spatial Vision, 10, 437-42. [full text]  157 cites  
pdf  Pelli, D. G., & Zhang, L. (1991) Accurate control of contrast on microcomputer displays. Vision Research 31, 1337-1350.  224 cites  

Tips — Advice for users of the Psychtoolbox and VideoToolbox.

pdf  Pelli, D. G. (1997) Pixel independence: measuring spatial interactions on a CRT display. Spatial Vision, 10, 443-446.  


Sloan font — Based on Louise Sloan’s design, which has been designated the US standard for acuity testing by the National Academy of Sciences, National Research Council, Committee on Vision (1980, Adv Ophthalmol, 41, 103-148. [PubMed]). Note that the standard specifies only CDHKNORSVZ, whereas the font file goes beyond that to provide a complete uppercase alphabet A-Z in a consistent style. The C is a Landolt C. The C and O are particularly hard to discriminate from each other, so some studies may wish to omit the C (see Elliott, Whitaker, & Bonette, 1990. Ophthalmic Physiol Opt, 10(4), 323-326. [PubMed]). This font was developed for the Pelli-Robson Contrast Sensitivity Chart. It is made available here for research purposes and may not be distributed further. Commercial use of this font would require a license from Denis Pelli. To download, choose version 1 or 2, as explained in the text document Sloan.rtf:
Version 1: Sloan for Macintosh (zip or stuffit archive) or Windows (zip archive). This is a PostScript Type 1 font, which you install like any other font.
Version 2: Sloan.otf is in the new universal Open Type font format, which is supported by more and more applications on Mac and Windows platforms.
Adobe provides installation instructions. Publications of research using any of these font files should cite:

pdf  Pelli, D. G., Robson, J. G., & Wilkins, A. J. (1988) The design of a new letter chart for measuring contrast sensitivity. Clinical Vision Sciences 2, 187-199.  287 cites  

Yung font — 26 Chinese characters a-z based on high-resolution scans of Yung Chih-sheng’s beautiful calligraphy in a beginning Chinese primer (DeFrancis, J., 1976, Character Text for Beginning Chinese, Second Ed. New Haven, CT: Yale University Press.). To download, choose a format: Yung for Macintosh (zip or stuffit archive) or Windows (zip archive). This is a PostScript Type 1 font, which you install like any other font. Adobe provides installation instructions. Publications of research using this font should cite:
pdf  Pelli, D. G., Burns, C. W., Farell, B., & Moore-Page, D. C. (2006) Detecting features and identifying letters. Vision Research, 46(28), 4646-4674. [PubMed]  

photoThe Daq Toolbox is a set of MATLAB functions providing communication with a particular USB data acquisition device (daq): the PMD-1208FS made by Measurement Computing. This daq costs $150 and offers "50 kHz" input and output 12-bit sampling of analog voltages (8 in, 2 out) and 16 digital i/o lines, with signals brought out to screw terminals. ("50 kHz" is a theoretical upper limit: as of 18 April 2005 we attain 2 kHz.) The PMD-1208FS is the size of a wallet and is powered through its USB cable. We have complete control of it from within MATLAB, via the PsychHID extension. The Daq Toolbox is free and can be downloaded from the Daq Toolbox web page. It is self-contained, and may be used with or without the rest of the Psychtoolbox. The only requirements are MATLAB, Mac OS X 10.3 or better, and a USB port to connect the PMD-1208FS.

AutoBrightness.applescript and AutoBrightness.m (click to download) allow you to turn off a pesky feature of Apple's liquid crystal displays. In Mac OS X, this feature is manually enabled/disabled by the "Automatically adjust brightness" checkbox in the System Preferences: Displays panel. While the feature is enabled, your Mac slowly adjusts the screen luminance of your Apple liquid crystal display, to track the luminance of the room. That's bad for screen calibration and perhaps also bad for your experiments. My AutoBrightness routines allow your programs to read the on/off setting of that feature, and enable or disable it. The Applescript will work from any application (e.g. MATLAB, Mathematica) that can send it to the Mac OS. The MATLAB routine merely calls the Applescript, and can easily be translated to any suitable language. For use in MATLAB, just put both files anywhere in MATLAB's path. I hope they will be added to the Psychtoolbox. May 29, 2015: IMPORTANT: A new "screenNumber" argument has been added, so any programs that called the older version will need to be edited to include that new argument. June 1, 2015: Cope with spaces in file path.

ScreenProfile.applescript and ScreenProfile.m (included in, click to download) get and set the name of the color profile used on one Macintosh screen. June 1, 2015: Cope with spaces in file path. June 3, 2015: Convert returned values to expected type.

ScriptingOk.applescript and ScriptingOk.m (included in, click to download) check whether your application has permission to control the computer through applescripts. ScriptingOkShowPermission also opens the relevant System Preferences Permission panel.

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