Abstract

Discrimination thresholds for velocity and contrast were measured as a function of (1) the stimulus duration, (2) the reference contrast of the stimuli, (3) the stimulus velocity, and (4) whether the observer knew on which dimension, velocity or contrast, the gratings would differ. Two vertically oriented grating patches were presented centered 2 deg left and right of the fixation point. The stimuli drifted under a stationary envelope to the right at a speed of either 1.25 deg/s (Experiment 1) or 5 deg/s (Experiment 2). The reference contrast was varied over five interleaved staircases from 0.02 to 0.32 in equal logarithmic steps. The results of two different tasks were compared. In the single-judgment task, the subject knew along which dimension the stimuli would change and was asked to judge which stimulus had the higher value along that dimension. In the dual-judgment task, the stimuli could differ in either velocity or contrast but not both. In this task the subject first indicated which dimension differed and second which stimulus had the higher value along that dimension. The dual-/single-judgment threshold ratios remained constant over a wide range of stimulus conditions. The mean value of these ratios, however, significantly exceeds that expected by the vector model presented by Greenlee and Thomas [J. Opt. Soc. Am. A 10, 395 (1993)]. A modification of the model, which assumes that velocity and contrast are not independently coded, appears to be sufficient to account for the observed differences. The results are in line with the known dependency of perceived speed on stimulus contrast.

© 1998 Optical Society of America

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  1. P. Thompson, “Perceived rate of movement depends on contrast,” Vision Res. 22, 377–380 (1982).
    [CrossRef] [PubMed]
  2. L. S. Stone, P. Thompson, “Human speed perception is contrast dependent,” Vision Res. 32, 1535–1549 (1992).
    [CrossRef] [PubMed]
  3. P. Thompson, L. S. Stone, S. Swash, “Speed estimates from grating patches are not contrast-normalized,” Vision Res. 36, 667–674 (1996).
    [CrossRef] [PubMed]
  4. R. Müller, M. W. Greenlee, “Effect of contrast and adaptation on the perception of the direction and speed of drifting gratings,” Vision Res. 34, 2071–2092 (1994).
    [CrossRef] [PubMed]
  5. M. A. Georgeson, “Apparent spatial frequency and contrast of gratings: separate effects of contrast and duration,” Vision Res. 25, 1721–1727 (1985).
    [CrossRef]
  6. E. T. Davis, P. Kramer, D. Yager, “Shifts in perceived spatial frequency of low-contrast stimuli: data and theory,” J. Opt. Soc. Am. A 3, 1189–1202 (1986).
    [CrossRef] [PubMed]
  7. D. G. Albrecht, D. B. Hamilton, “Striate cortex of monkey and cat: contrast response function,” J. Neurophysiol. 48, 217–237 (1982).
    [PubMed]
  8. G. Sclar, J. H. R. Maunsell, P. Lennie, “Coding of image contrast in central visual pathways of the macaque monkey,” Vision Res. 30, 1–10 (1990).
    [CrossRef] [PubMed]
  9. S. A. Klein, “Double-judgment psychophysics: problems and solutions,” J. Opt. Soc. Am. A 2, 1560–1585 (1985).
    [CrossRef] [PubMed]
  10. J. P. Thomas, L. A. Olzak, “Simultaneous detection and identification,” in Simultaneous Detection and Identification, F. G. Ashby, ed. (Erlbaum, Hillsdale, N.J.,1992), pp. 254–277.
  11. M. W. Greenlee, J. P. Thomas, “Simultaneous discrimination of the spatial frequency and contrast of periodic stimuli,” J. Opt. Soc. Am. A 10, 395–404 (1993).
    [CrossRef] [PubMed]
  12. E. T. Davis, P. Kramer, N. Graham, “Uncertainty about spatial frequency, spatial position, or contrast of visual patterns,” Percept. Psychophys. 33, 20–28 (1983).
    [CrossRef] [PubMed]
  13. D. G. Pelli, “Uncertainty effects explain many aspects of visual contrast detection and discrimination,” J. Opt. Soc. Am. A 2, 1508–1531 (1985).
    [CrossRef] [PubMed]
  14. N. Graham, Visual Pattern Analyzers (Oxford U. Press, New York, 1989).
  15. J. P. Thomas, J. Gille, R. A. Barker, “Simultaneous visual detection and identification: theory and data,” J. Opt. Soc. Am. 72, 1642–1651 (1982).
    [CrossRef] [PubMed]
  16. J. P. Thomas, “Underlying psychometric functions for detecting gratings and identifying spatial frequency,” J. Opt. Soc. Am. 73, 751–758 (1983).
    [CrossRef] [PubMed]
  17. W. P. Tanner, “Theory of recognition,” J. Acoust. Soc. Am. 28, 882–888 (1956).
    [CrossRef]
  18. H. Lieberman, A. P. Pentland, “Microcomputer-based estimation of psychophysical thresholds: the best PEST,” Behav. Res. Methods Instrum. 14, 21–25 (1982).
    [CrossRef]
  19. P. Thompson, “Discrimination of moving gratings at and above detection threshold,” Vision Res. 23, 1533–1538 (1983).
    [CrossRef] [PubMed]
  20. P. Thompson, “The coding of velocity of movement in the human visual system,” Vision Res. 24, 41–45 (1984).
    [CrossRef] [PubMed]
  21. R. Müller, E. Göpfert, M. Hartwig, “VEP-Untersuchungen zur Kodierung der Geschwindigkeit bewegter Streifenmuster im Kortex des Menschen,” Z. EEG-EMG 16, 75–80 (1985).
  22. G. A. Orban, J. de Wolf, H. Maes, “Factors influencing velocity coding in the human visual system,” Vision Res. 24, 33–39 (1984).
    [CrossRef] [PubMed]
  23. R. F. Hess, R. J. Snowden, “Temporal properties of human visual filters: number, shapes and spatial covariation,” Vision Res. 32, 47–59 (1992).
    [CrossRef] [PubMed]
  24. J. Yang, S. B. Stevenson, “Effects of spatial frequency, duration, and contrast on discriminating motion directions,” J. Opt. Soc. Am. A 14, 2041–2048 (1997).
    [CrossRef]
  25. These distributions are significantly different from that expected by chance. Observer RM showed error distributions that significantly differ from that of the guessing model (speed: chi2=8.5,df=2,p<0.02; contrast: chi2=40.6,df=2,p<0.001) but also differ from that expected by the vector model (speed: chi2=35.7,df=2,p<0.001; contrast: chi2=4.7,df=2,p<0.1). Likewise, observer ES exhibited error distributions that deviate from those expected by the guessing model (speed: chi2 =327.3,df=2,p<0.001; contrast: chi2=116.9,df =2,p<0.001) and the vector model (speed: chi2=116.0,df=2,p<0.001; contrast: chi2=210.5,df=2,p<0.001).
  26. Observer RM showed error distributions that significantly differ from that of the guessing model (speed: chi2=46.3,df=2,p<0.001; contrast: chi2=147.7,df=2,p<0.001) but also deviate from that expected by the vector model (speed: chi2=60.4,df=2,p<0.001; contrast: chi2=9.6,df=2,p<0.01). In similar fashion observer ES exhibited error distributions that deviate from those expected by the guessing model (speed: chi2=179.2,df=2,p<0.001; contrast: chi2=88.4,df=2,p<0.001) and the vector model (speed: chi2=38.4,df=2,p<0.001; contrast: chi2=213.8,df=2,p<0.001). Also, observer GM showed error distributions that deviate from those expected by both models: guessing (speed: chi2=100.1,df=2,p<0.001; contrast: chi2=147.5;df=2,p<0.001) and vector (speed: chi2=51.7,df=2,p<0.001; contrast: chi2=18.4,df=2,p<0.001).
  27. S. Magnussen, M. W. Greenlee, J. P. Thomas, “Parallel processing in visual short-term memory,” J. Exp. Psychol. 22, 202–212 (1996).
  28. S. Magnussen, M. W. Greenlee, “Retention and disruption of motion information in visual short-term memory,” J. Exp. Psychol. 18, 151–156 (1992).
  29. S. P. McKee, G. H. Silverman, K. Nakayama, “Precise velocity discrimination despite random variations in temporal frequency and contrast,” Vision Res. 26, 609–619 (1986).
    [CrossRef] [PubMed]
  30. A. T. Smith, “Velocity perception and discrimination: relation to temporal mechanisms,” Vision Res. 27, 1491–1500 (1987).
    [CrossRef] [PubMed]
  31. A. T. Smith, G. K. Edgar, “The separability of temporal frequency and velocity,” Vision Res. 31, 321–326 (1991).
    [CrossRef] [PubMed]
  32. Y. Chen, H. E. Bedell, L. J. Frishman, “Velocity discrimination between stimuli of different spatial frequencies,” Invest. Ophthalmol. Visual Sci. 36, S54 (1995).
  33. S. Magnussen, M. W. Greenlee, “Competition and sharing of processing resources in visual discrimination,” J. Exp. Psychol. 23, 1603–1616 (1997).
  34. C. Yo, H. R. Wilson, “Peripheral temporal frequency channels code frequency and speed inaccurately but allow accurate discrimination,” Vision Res. 33, 33–45 (1993).
    [CrossRef] [PubMed]

1997 (2)

S. Magnussen, M. W. Greenlee, “Competition and sharing of processing resources in visual discrimination,” J. Exp. Psychol. 23, 1603–1616 (1997).

J. Yang, S. B. Stevenson, “Effects of spatial frequency, duration, and contrast on discriminating motion directions,” J. Opt. Soc. Am. A 14, 2041–2048 (1997).
[CrossRef]

1996 (2)

P. Thompson, L. S. Stone, S. Swash, “Speed estimates from grating patches are not contrast-normalized,” Vision Res. 36, 667–674 (1996).
[CrossRef] [PubMed]

S. Magnussen, M. W. Greenlee, J. P. Thomas, “Parallel processing in visual short-term memory,” J. Exp. Psychol. 22, 202–212 (1996).

1995 (1)

Y. Chen, H. E. Bedell, L. J. Frishman, “Velocity discrimination between stimuli of different spatial frequencies,” Invest. Ophthalmol. Visual Sci. 36, S54 (1995).

1994 (1)

R. Müller, M. W. Greenlee, “Effect of contrast and adaptation on the perception of the direction and speed of drifting gratings,” Vision Res. 34, 2071–2092 (1994).
[CrossRef] [PubMed]

1993 (2)

C. Yo, H. R. Wilson, “Peripheral temporal frequency channels code frequency and speed inaccurately but allow accurate discrimination,” Vision Res. 33, 33–45 (1993).
[CrossRef] [PubMed]

M. W. Greenlee, J. P. Thomas, “Simultaneous discrimination of the spatial frequency and contrast of periodic stimuli,” J. Opt. Soc. Am. A 10, 395–404 (1993).
[CrossRef] [PubMed]

1992 (3)

L. S. Stone, P. Thompson, “Human speed perception is contrast dependent,” Vision Res. 32, 1535–1549 (1992).
[CrossRef] [PubMed]

S. Magnussen, M. W. Greenlee, “Retention and disruption of motion information in visual short-term memory,” J. Exp. Psychol. 18, 151–156 (1992).

R. F. Hess, R. J. Snowden, “Temporal properties of human visual filters: number, shapes and spatial covariation,” Vision Res. 32, 47–59 (1992).
[CrossRef] [PubMed]

1991 (1)

A. T. Smith, G. K. Edgar, “The separability of temporal frequency and velocity,” Vision Res. 31, 321–326 (1991).
[CrossRef] [PubMed]

1990 (1)

G. Sclar, J. H. R. Maunsell, P. Lennie, “Coding of image contrast in central visual pathways of the macaque monkey,” Vision Res. 30, 1–10 (1990).
[CrossRef] [PubMed]

1987 (1)

A. T. Smith, “Velocity perception and discrimination: relation to temporal mechanisms,” Vision Res. 27, 1491–1500 (1987).
[CrossRef] [PubMed]

1986 (2)

E. T. Davis, P. Kramer, D. Yager, “Shifts in perceived spatial frequency of low-contrast stimuli: data and theory,” J. Opt. Soc. Am. A 3, 1189–1202 (1986).
[CrossRef] [PubMed]

S. P. McKee, G. H. Silverman, K. Nakayama, “Precise velocity discrimination despite random variations in temporal frequency and contrast,” Vision Res. 26, 609–619 (1986).
[CrossRef] [PubMed]

1985 (4)

R. Müller, E. Göpfert, M. Hartwig, “VEP-Untersuchungen zur Kodierung der Geschwindigkeit bewegter Streifenmuster im Kortex des Menschen,” Z. EEG-EMG 16, 75–80 (1985).

M. A. Georgeson, “Apparent spatial frequency and contrast of gratings: separate effects of contrast and duration,” Vision Res. 25, 1721–1727 (1985).
[CrossRef]

D. G. Pelli, “Uncertainty effects explain many aspects of visual contrast detection and discrimination,” J. Opt. Soc. Am. A 2, 1508–1531 (1985).
[CrossRef] [PubMed]

S. A. Klein, “Double-judgment psychophysics: problems and solutions,” J. Opt. Soc. Am. A 2, 1560–1585 (1985).
[CrossRef] [PubMed]

1984 (2)

G. A. Orban, J. de Wolf, H. Maes, “Factors influencing velocity coding in the human visual system,” Vision Res. 24, 33–39 (1984).
[CrossRef] [PubMed]

P. Thompson, “The coding of velocity of movement in the human visual system,” Vision Res. 24, 41–45 (1984).
[CrossRef] [PubMed]

1983 (3)

P. Thompson, “Discrimination of moving gratings at and above detection threshold,” Vision Res. 23, 1533–1538 (1983).
[CrossRef] [PubMed]

E. T. Davis, P. Kramer, N. Graham, “Uncertainty about spatial frequency, spatial position, or contrast of visual patterns,” Percept. Psychophys. 33, 20–28 (1983).
[CrossRef] [PubMed]

J. P. Thomas, “Underlying psychometric functions for detecting gratings and identifying spatial frequency,” J. Opt. Soc. Am. 73, 751–758 (1983).
[CrossRef] [PubMed]

1982 (4)

J. P. Thomas, J. Gille, R. A. Barker, “Simultaneous visual detection and identification: theory and data,” J. Opt. Soc. Am. 72, 1642–1651 (1982).
[CrossRef] [PubMed]

H. Lieberman, A. P. Pentland, “Microcomputer-based estimation of psychophysical thresholds: the best PEST,” Behav. Res. Methods Instrum. 14, 21–25 (1982).
[CrossRef]

D. G. Albrecht, D. B. Hamilton, “Striate cortex of monkey and cat: contrast response function,” J. Neurophysiol. 48, 217–237 (1982).
[PubMed]

P. Thompson, “Perceived rate of movement depends on contrast,” Vision Res. 22, 377–380 (1982).
[CrossRef] [PubMed]

1956 (1)

W. P. Tanner, “Theory of recognition,” J. Acoust. Soc. Am. 28, 882–888 (1956).
[CrossRef]

Albrecht, D. G.

D. G. Albrecht, D. B. Hamilton, “Striate cortex of monkey and cat: contrast response function,” J. Neurophysiol. 48, 217–237 (1982).
[PubMed]

Barker, R. A.

Bedell, H. E.

Y. Chen, H. E. Bedell, L. J. Frishman, “Velocity discrimination between stimuli of different spatial frequencies,” Invest. Ophthalmol. Visual Sci. 36, S54 (1995).

Chen, Y.

Y. Chen, H. E. Bedell, L. J. Frishman, “Velocity discrimination between stimuli of different spatial frequencies,” Invest. Ophthalmol. Visual Sci. 36, S54 (1995).

Davis, E. T.

E. T. Davis, P. Kramer, D. Yager, “Shifts in perceived spatial frequency of low-contrast stimuli: data and theory,” J. Opt. Soc. Am. A 3, 1189–1202 (1986).
[CrossRef] [PubMed]

E. T. Davis, P. Kramer, N. Graham, “Uncertainty about spatial frequency, spatial position, or contrast of visual patterns,” Percept. Psychophys. 33, 20–28 (1983).
[CrossRef] [PubMed]

de Wolf, J.

G. A. Orban, J. de Wolf, H. Maes, “Factors influencing velocity coding in the human visual system,” Vision Res. 24, 33–39 (1984).
[CrossRef] [PubMed]

Edgar, G. K.

A. T. Smith, G. K. Edgar, “The separability of temporal frequency and velocity,” Vision Res. 31, 321–326 (1991).
[CrossRef] [PubMed]

Frishman, L. J.

Y. Chen, H. E. Bedell, L. J. Frishman, “Velocity discrimination between stimuli of different spatial frequencies,” Invest. Ophthalmol. Visual Sci. 36, S54 (1995).

Georgeson, M. A.

M. A. Georgeson, “Apparent spatial frequency and contrast of gratings: separate effects of contrast and duration,” Vision Res. 25, 1721–1727 (1985).
[CrossRef]

Gille, J.

Göpfert, E.

R. Müller, E. Göpfert, M. Hartwig, “VEP-Untersuchungen zur Kodierung der Geschwindigkeit bewegter Streifenmuster im Kortex des Menschen,” Z. EEG-EMG 16, 75–80 (1985).

Graham, N.

E. T. Davis, P. Kramer, N. Graham, “Uncertainty about spatial frequency, spatial position, or contrast of visual patterns,” Percept. Psychophys. 33, 20–28 (1983).
[CrossRef] [PubMed]

N. Graham, Visual Pattern Analyzers (Oxford U. Press, New York, 1989).

Greenlee, M. W.

S. Magnussen, M. W. Greenlee, “Competition and sharing of processing resources in visual discrimination,” J. Exp. Psychol. 23, 1603–1616 (1997).

S. Magnussen, M. W. Greenlee, J. P. Thomas, “Parallel processing in visual short-term memory,” J. Exp. Psychol. 22, 202–212 (1996).

R. Müller, M. W. Greenlee, “Effect of contrast and adaptation on the perception of the direction and speed of drifting gratings,” Vision Res. 34, 2071–2092 (1994).
[CrossRef] [PubMed]

M. W. Greenlee, J. P. Thomas, “Simultaneous discrimination of the spatial frequency and contrast of periodic stimuli,” J. Opt. Soc. Am. A 10, 395–404 (1993).
[CrossRef] [PubMed]

S. Magnussen, M. W. Greenlee, “Retention and disruption of motion information in visual short-term memory,” J. Exp. Psychol. 18, 151–156 (1992).

Hamilton, D. B.

D. G. Albrecht, D. B. Hamilton, “Striate cortex of monkey and cat: contrast response function,” J. Neurophysiol. 48, 217–237 (1982).
[PubMed]

Hartwig, M.

R. Müller, E. Göpfert, M. Hartwig, “VEP-Untersuchungen zur Kodierung der Geschwindigkeit bewegter Streifenmuster im Kortex des Menschen,” Z. EEG-EMG 16, 75–80 (1985).

Hess, R. F.

R. F. Hess, R. J. Snowden, “Temporal properties of human visual filters: number, shapes and spatial covariation,” Vision Res. 32, 47–59 (1992).
[CrossRef] [PubMed]

Klein, S. A.

Kramer, P.

E. T. Davis, P. Kramer, D. Yager, “Shifts in perceived spatial frequency of low-contrast stimuli: data and theory,” J. Opt. Soc. Am. A 3, 1189–1202 (1986).
[CrossRef] [PubMed]

E. T. Davis, P. Kramer, N. Graham, “Uncertainty about spatial frequency, spatial position, or contrast of visual patterns,” Percept. Psychophys. 33, 20–28 (1983).
[CrossRef] [PubMed]

Lennie, P.

G. Sclar, J. H. R. Maunsell, P. Lennie, “Coding of image contrast in central visual pathways of the macaque monkey,” Vision Res. 30, 1–10 (1990).
[CrossRef] [PubMed]

Lieberman, H.

H. Lieberman, A. P. Pentland, “Microcomputer-based estimation of psychophysical thresholds: the best PEST,” Behav. Res. Methods Instrum. 14, 21–25 (1982).
[CrossRef]

Maes, H.

G. A. Orban, J. de Wolf, H. Maes, “Factors influencing velocity coding in the human visual system,” Vision Res. 24, 33–39 (1984).
[CrossRef] [PubMed]

Magnussen, S.

S. Magnussen, M. W. Greenlee, “Competition and sharing of processing resources in visual discrimination,” J. Exp. Psychol. 23, 1603–1616 (1997).

S. Magnussen, M. W. Greenlee, J. P. Thomas, “Parallel processing in visual short-term memory,” J. Exp. Psychol. 22, 202–212 (1996).

S. Magnussen, M. W. Greenlee, “Retention and disruption of motion information in visual short-term memory,” J. Exp. Psychol. 18, 151–156 (1992).

Maunsell, J. H. R.

G. Sclar, J. H. R. Maunsell, P. Lennie, “Coding of image contrast in central visual pathways of the macaque monkey,” Vision Res. 30, 1–10 (1990).
[CrossRef] [PubMed]

McKee, S. P.

S. P. McKee, G. H. Silverman, K. Nakayama, “Precise velocity discrimination despite random variations in temporal frequency and contrast,” Vision Res. 26, 609–619 (1986).
[CrossRef] [PubMed]

Müller, R.

R. Müller, M. W. Greenlee, “Effect of contrast and adaptation on the perception of the direction and speed of drifting gratings,” Vision Res. 34, 2071–2092 (1994).
[CrossRef] [PubMed]

R. Müller, E. Göpfert, M. Hartwig, “VEP-Untersuchungen zur Kodierung der Geschwindigkeit bewegter Streifenmuster im Kortex des Menschen,” Z. EEG-EMG 16, 75–80 (1985).

Nakayama, K.

S. P. McKee, G. H. Silverman, K. Nakayama, “Precise velocity discrimination despite random variations in temporal frequency and contrast,” Vision Res. 26, 609–619 (1986).
[CrossRef] [PubMed]

Olzak, L. A.

J. P. Thomas, L. A. Olzak, “Simultaneous detection and identification,” in Simultaneous Detection and Identification, F. G. Ashby, ed. (Erlbaum, Hillsdale, N.J.,1992), pp. 254–277.

Orban, G. A.

G. A. Orban, J. de Wolf, H. Maes, “Factors influencing velocity coding in the human visual system,” Vision Res. 24, 33–39 (1984).
[CrossRef] [PubMed]

Pelli, D. G.

Pentland, A. P.

H. Lieberman, A. P. Pentland, “Microcomputer-based estimation of psychophysical thresholds: the best PEST,” Behav. Res. Methods Instrum. 14, 21–25 (1982).
[CrossRef]

Sclar, G.

G. Sclar, J. H. R. Maunsell, P. Lennie, “Coding of image contrast in central visual pathways of the macaque monkey,” Vision Res. 30, 1–10 (1990).
[CrossRef] [PubMed]

Silverman, G. H.

S. P. McKee, G. H. Silverman, K. Nakayama, “Precise velocity discrimination despite random variations in temporal frequency and contrast,” Vision Res. 26, 609–619 (1986).
[CrossRef] [PubMed]

Smith, A. T.

A. T. Smith, G. K. Edgar, “The separability of temporal frequency and velocity,” Vision Res. 31, 321–326 (1991).
[CrossRef] [PubMed]

A. T. Smith, “Velocity perception and discrimination: relation to temporal mechanisms,” Vision Res. 27, 1491–1500 (1987).
[CrossRef] [PubMed]

Snowden, R. J.

R. F. Hess, R. J. Snowden, “Temporal properties of human visual filters: number, shapes and spatial covariation,” Vision Res. 32, 47–59 (1992).
[CrossRef] [PubMed]

Stevenson, S. B.

Stone, L. S.

P. Thompson, L. S. Stone, S. Swash, “Speed estimates from grating patches are not contrast-normalized,” Vision Res. 36, 667–674 (1996).
[CrossRef] [PubMed]

L. S. Stone, P. Thompson, “Human speed perception is contrast dependent,” Vision Res. 32, 1535–1549 (1992).
[CrossRef] [PubMed]

Swash, S.

P. Thompson, L. S. Stone, S. Swash, “Speed estimates from grating patches are not contrast-normalized,” Vision Res. 36, 667–674 (1996).
[CrossRef] [PubMed]

Tanner, W. P.

W. P. Tanner, “Theory of recognition,” J. Acoust. Soc. Am. 28, 882–888 (1956).
[CrossRef]

Thomas, J. P.

Thompson, P.

P. Thompson, L. S. Stone, S. Swash, “Speed estimates from grating patches are not contrast-normalized,” Vision Res. 36, 667–674 (1996).
[CrossRef] [PubMed]

L. S. Stone, P. Thompson, “Human speed perception is contrast dependent,” Vision Res. 32, 1535–1549 (1992).
[CrossRef] [PubMed]

P. Thompson, “The coding of velocity of movement in the human visual system,” Vision Res. 24, 41–45 (1984).
[CrossRef] [PubMed]

P. Thompson, “Discrimination of moving gratings at and above detection threshold,” Vision Res. 23, 1533–1538 (1983).
[CrossRef] [PubMed]

P. Thompson, “Perceived rate of movement depends on contrast,” Vision Res. 22, 377–380 (1982).
[CrossRef] [PubMed]

Wilson, H. R.

C. Yo, H. R. Wilson, “Peripheral temporal frequency channels code frequency and speed inaccurately but allow accurate discrimination,” Vision Res. 33, 33–45 (1993).
[CrossRef] [PubMed]

Yager, D.

Yang, J.

Yo, C.

C. Yo, H. R. Wilson, “Peripheral temporal frequency channels code frequency and speed inaccurately but allow accurate discrimination,” Vision Res. 33, 33–45 (1993).
[CrossRef] [PubMed]

Behav. Res. Methods Instrum. (1)

H. Lieberman, A. P. Pentland, “Microcomputer-based estimation of psychophysical thresholds: the best PEST,” Behav. Res. Methods Instrum. 14, 21–25 (1982).
[CrossRef]

Invest. Ophthalmol. Visual Sci. (1)

Y. Chen, H. E. Bedell, L. J. Frishman, “Velocity discrimination between stimuli of different spatial frequencies,” Invest. Ophthalmol. Visual Sci. 36, S54 (1995).

J. Acoust. Soc. Am. (1)

W. P. Tanner, “Theory of recognition,” J. Acoust. Soc. Am. 28, 882–888 (1956).
[CrossRef]

J. Exp. Psychol. (3)

S. Magnussen, M. W. Greenlee, “Competition and sharing of processing resources in visual discrimination,” J. Exp. Psychol. 23, 1603–1616 (1997).

S. Magnussen, M. W. Greenlee, J. P. Thomas, “Parallel processing in visual short-term memory,” J. Exp. Psychol. 22, 202–212 (1996).

S. Magnussen, M. W. Greenlee, “Retention and disruption of motion information in visual short-term memory,” J. Exp. Psychol. 18, 151–156 (1992).

J. Neurophysiol. (1)

D. G. Albrecht, D. B. Hamilton, “Striate cortex of monkey and cat: contrast response function,” J. Neurophysiol. 48, 217–237 (1982).
[PubMed]

J. Opt. Soc. Am. (2)

J. Opt. Soc. Am. A (5)

Percept. Psychophys. (1)

E. T. Davis, P. Kramer, N. Graham, “Uncertainty about spatial frequency, spatial position, or contrast of visual patterns,” Percept. Psychophys. 33, 20–28 (1983).
[CrossRef] [PubMed]

Vision Res. (14)

G. Sclar, J. H. R. Maunsell, P. Lennie, “Coding of image contrast in central visual pathways of the macaque monkey,” Vision Res. 30, 1–10 (1990).
[CrossRef] [PubMed]

C. Yo, H. R. Wilson, “Peripheral temporal frequency channels code frequency and speed inaccurately but allow accurate discrimination,” Vision Res. 33, 33–45 (1993).
[CrossRef] [PubMed]

S. P. McKee, G. H. Silverman, K. Nakayama, “Precise velocity discrimination despite random variations in temporal frequency and contrast,” Vision Res. 26, 609–619 (1986).
[CrossRef] [PubMed]

A. T. Smith, “Velocity perception and discrimination: relation to temporal mechanisms,” Vision Res. 27, 1491–1500 (1987).
[CrossRef] [PubMed]

A. T. Smith, G. K. Edgar, “The separability of temporal frequency and velocity,” Vision Res. 31, 321–326 (1991).
[CrossRef] [PubMed]

G. A. Orban, J. de Wolf, H. Maes, “Factors influencing velocity coding in the human visual system,” Vision Res. 24, 33–39 (1984).
[CrossRef] [PubMed]

R. F. Hess, R. J. Snowden, “Temporal properties of human visual filters: number, shapes and spatial covariation,” Vision Res. 32, 47–59 (1992).
[CrossRef] [PubMed]

P. Thompson, “Discrimination of moving gratings at and above detection threshold,” Vision Res. 23, 1533–1538 (1983).
[CrossRef] [PubMed]

P. Thompson, “The coding of velocity of movement in the human visual system,” Vision Res. 24, 41–45 (1984).
[CrossRef] [PubMed]

P. Thompson, “Perceived rate of movement depends on contrast,” Vision Res. 22, 377–380 (1982).
[CrossRef] [PubMed]

L. S. Stone, P. Thompson, “Human speed perception is contrast dependent,” Vision Res. 32, 1535–1549 (1992).
[CrossRef] [PubMed]

P. Thompson, L. S. Stone, S. Swash, “Speed estimates from grating patches are not contrast-normalized,” Vision Res. 36, 667–674 (1996).
[CrossRef] [PubMed]

R. Müller, M. W. Greenlee, “Effect of contrast and adaptation on the perception of the direction and speed of drifting gratings,” Vision Res. 34, 2071–2092 (1994).
[CrossRef] [PubMed]

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[CrossRef]

Z. EEG-EMG (1)

R. Müller, E. Göpfert, M. Hartwig, “VEP-Untersuchungen zur Kodierung der Geschwindigkeit bewegter Streifenmuster im Kortex des Menschen,” Z. EEG-EMG 16, 75–80 (1985).

Other (4)

These distributions are significantly different from that expected by chance. Observer RM showed error distributions that significantly differ from that of the guessing model (speed: chi2=8.5,df=2,p<0.02; contrast: chi2=40.6,df=2,p<0.001) but also differ from that expected by the vector model (speed: chi2=35.7,df=2,p<0.001; contrast: chi2=4.7,df=2,p<0.1). Likewise, observer ES exhibited error distributions that deviate from those expected by the guessing model (speed: chi2 =327.3,df=2,p<0.001; contrast: chi2=116.9,df =2,p<0.001) and the vector model (speed: chi2=116.0,df=2,p<0.001; contrast: chi2=210.5,df=2,p<0.001).

Observer RM showed error distributions that significantly differ from that of the guessing model (speed: chi2=46.3,df=2,p<0.001; contrast: chi2=147.7,df=2,p<0.001) but also deviate from that expected by the vector model (speed: chi2=60.4,df=2,p<0.001; contrast: chi2=9.6,df=2,p<0.01). In similar fashion observer ES exhibited error distributions that deviate from those expected by the guessing model (speed: chi2=179.2,df=2,p<0.001; contrast: chi2=88.4,df=2,p<0.001) and the vector model (speed: chi2=38.4,df=2,p<0.001; contrast: chi2=213.8,df=2,p<0.001). Also, observer GM showed error distributions that deviate from those expected by both models: guessing (speed: chi2=100.1,df=2,p<0.001; contrast: chi2=147.5;df=2,p<0.001) and vector (speed: chi2=51.7,df=2,p<0.001; contrast: chi2=18.4,df=2,p<0.001).

J. P. Thomas, L. A. Olzak, “Simultaneous detection and identification,” in Simultaneous Detection and Identification, F. G. Ashby, ed. (Erlbaum, Hillsdale, N.J.,1992), pp. 254–277.

N. Graham, Visual Pattern Analyzers (Oxford U. Press, New York, 1989).

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Figures (8)

Fig. 1
Fig. 1

Schematic illustration of the experimental design in which the single- and dual-judgment tasks are shown. One of the stimuli, the reference stimulus, had a constant speed and a contrast that could vary over five steps (0.02, 0.04, 0.08, 0.16, and 0.32 across individual staircases). The other stimulus, the test stimulus, differed from the reference stimulus either in speed or in contrast. In the single-judgment task, the stimuli could vary in only one of the two dimensions, and the subject judged which stimulus had the higher value along that dimension. In the dual-judgment task, the stimuli varied along one or the other dimension, and the subject first had to decide which dimension was different and then which stimulus had the higher value along that dimension.

Fig. 2
Fig. 2

Discrimination thresholds as a function of reference contrast for observer RM at a speed of 1.25 deg/s. Symbols represent thresholds measured for four time constants (see the legend). Data points are the arithmetic mean values of six runs. Error bars show the standard error of the mean. (a) Velocity discrimination thresholds (Δv/v) measured in the single-judgment task, (b) Δv/v measured in the dual-judgment task, (c) contrast discrimination thresholds (Δc/c) measured in the single-judgment task, (d) Δc/c measured in the dual-judgment task.

Fig. 3
Fig. 3

Results for observer ES (six runs). Symbols present thresholds measured for three time constants (see the legend). Otherwise, as in Fig. 2.

Fig. 4
Fig. 4

Weber ratios obtained in the dual-judgment task plotted against Weber ratios of the single-judgment task on log–log coordinates. Reference speed was 1.25 deg/s. Symbols represent the results for different time constants, and each point represents the geometric mean value of six independent runs for one of five reference contrasts. Error bars show +1 standard errors for single judgment (horizontal bars) and dual judgment (vertical bars). Values are shown in (a) and (b) for observer RM for velocity and contrast discrimination, respectively, and likewise in (c) and (d) for observer ES. The dashed lines indicate the value of threshold elevation predicted by the vector model of Greenlee and Thomas.11

Fig. 5
Fig. 5

Wdual [Eq. (4)] plotted against Wsingle [Eq. (3)] on log–log coordinates. Reference speed was 1.25 deg/s. The results of observer RM are shown in (a), and those from observer ES in (b). Symbols present the results for different time constants. Each point represents the geometric mean value of six runs for each of five reference contrast levels. Error bars show +1 standard errors for single judgment (horizontal bars) and dual judgment (vertical bars). The dashed lines indicate the value of threshold elevation predicted by the vector model of Greenlee and Thomas.11

Fig. 6
Fig. 6

Discrimination thresholds as a function of reference contrast for observer RM. Reference speed was 5 deg/s. Data points present the arithmetic mean values of nine independent runs. Otherwise, as in Fig. 2.

Fig. 7
Fig. 7

Weber ratios for velocity and contrast discrimination are presented for observers RM [(a), (b); nine runs], ES [(c), (d); six runs], and GM [(e), (f); six runs]. Reference speed was 5 deg/s. Otherwise, as in Fig. 4.

Fig. 8
Fig. 8

Wdual [Eq. (4)] plotted against Wsingle [Eq. (3)] for a stimulus speed of 5.0 deg/s. Results are presented for (a) observer RM (nine runs), (b) observer ES (six runs), and (c) observer GM (six runs). Otherwise, as in Fig. 5.

Tables (3)

Tables Icon

Table 1 Response Distribution (in %) Observed in the Dual-Judgment Task for Velocity v and Contrast c (Collapsed over Five Reference Contrasts of Six Runs Each), with Error Rates Shown for the Three Error Types and for Reference Speed=1.25 deg/s

Tables Icon

Table 2 Geometric Mean and Lower Limit of the Confidence Interval (t test, p=0.05) of the Thomas Ratios T for Two Observers, for Reference Speed=1.25 deg/s

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Table 3 Geometric Mean and Lower Limit of the Confidence Interval (t test, p=0.05) of the Thomas Ratios T for Three Observers, for Reference Speed=5.0 deg/s

Equations (6)

Equations on this page are rendered with MathJax. Learn more.

W=Δw/w,
T=Wdual/Wsingle,
Wsingle=[(Δv/v)single(Δc/c)single]1/2,
Wdual=[(Δv/v)dual(Δc/c)dual]1/2.
T=Wdual/Wsingle.
ErrortypeI:correctdimension,incorrectstimulus4.5%,ErrortypeII:incorrectdimension,correctstimulus16.5%,ErrortypeIII:incorrectdimension,incorrectstimulus16.5%,

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