Abstract

Contour interaction, the detrimental effect of flanking features on the discrimination of optotypes, has been studied mainly close to the visual acuity limit. We were interested to know how these results compare with those for the detection of targets. According to the simplest model of contour interaction, comparable detection effects would be expected. The case for low-level masking would be further strengthened if the form and nature of the dependence on flank separation and flank polarity followed that typically found in studies of lateral spatial masking [Vision Res. 33, 993 (1993)]. Landolt Cs subtending a visual angle of 0.25°, 0.5°, and 1.0° were presented and contrast thresholds for detecting the presence of the Landolt C and discriminating its orientation were measured in five normal subjects as a function of flank separation and flank polarity. The results obtained for the relationship between detection and discrimination depend on the size of the target used. For small letters, discrimination but not detection was significantly affected by flanking bars. For large letters, detection and discrimination were affected to the same extent. However, in this case the effectiveness of opposite-polarity flanks and the finding that facilitation occurred at close, not far, flank separations suggests that the simplest explanation in terms of masking may not be applicable.

© 2005 Optical Society of America

Full Article  |  PDF Article

References

  • View by:
  • |
  • |
  • |

  1. M. C. Flom, F. W. Weymouth, D. Kahneman, “Visual resolution and contour interaction,” J. Opt. Soc. Am. 53, 1026–1032 (1963).
    [CrossRef] [PubMed]
  2. J. A. Stuart, H. M. Burian, “A study of separation difficulty: its relationship to visual acuity in normal and amblyopic eyes,” Am. J. Ophthalmol. 53, 471–477 (1962).
    [PubMed]
  3. W. Korte, “Über die Gestaltauffasssung im indirekten Sehen,” Z. Psychol. 93, 17–82 (1923).
  4. H. Bouma, “Interaction effects in parafoveal letter recognition,” Nature (London) 226, 177–178 (1970).
    [CrossRef]
  5. P. Müller, “Über das Sehen der Amblyopen,” Ophthalmologica 121, 143–149 (1951).
    [CrossRef]
  6. S. T. L. Chung, D. M. Levi, G. E. Legge, “Spatial-frequency and contrast properties of crowding,” Vision Res. 41, 1833–1850 (2001).
    [CrossRef] [PubMed]
  7. A. Toet, D. M. Levi, “The two-dimensional shape of spatial interaction zones in the parafovea,” Vision Res. 32, 1349–1357 (1992).
    [CrossRef] [PubMed]
  8. H. Strasburger, L. O. Harvey, I. Rentschler, “Contrast thresholds for identification of numeric characters in direct and eccentric view,” Percept. Psychophys. 49, 495–508 (1991).
    [CrossRef] [PubMed]
  9. S. J. Leat, W. Li, K. Epp, “Crowding in central and eccentric vision: the effects of contour interaction and attention,” Invest. Ophthalmol. Visual Sci. 40, 504–512 (1999).
  10. U. Polat, D. Sagi, “Lateral interactions between spatial channels: suppression and facilitation revealed by lateral masking experiments,” Vision Res. 33, 993–999 (1993).
    [CrossRef] [PubMed]
  11. C. B. Williams, R. F. Hess, “Relationship between facilitation at threshold and suprathreshold contour integration,” J. Opt. Soc. Am. A 15, 2046–2051 (1998).
    [CrossRef]
  12. J. A. Solomon, A. B. Watson, M. J. Morgan, “Transducer model produces facilitation from opposite-sign flanks,” Vision Res. 39, 987–992 (1999).
    [CrossRef] [PubMed]
  13. M. Palomares, M. C. LaPutt, D. G. Pelli, “Crowding is unlike masking,” Invest. Ophthalmol. Visual Sci. (Suppl.) 40, 351 (1999).
  14. J. A. Solomon, M. Morgan, “Flanked targets: easier to see, harder to identify,” Perception (Suppl.) 32, 47 (2003).
  15. D. M. Levi, S. A. Klein, S. Hariharan, “Suppressive and facilitatory spatial interactions in foveal vision: foveal crowding is simple contrast masking,” J. Vision 2, 140–166 (2002), p. 140.
  16. R. J. Jacobs, “Visual resolution and contour interaction in the fovea and periphery,” Vision Res. 19, 1187–1195 (1979).
    [CrossRef] [PubMed]
  17. A. J. Simmers, L. S. Gray, P. V. McGraw, B. Winn, “Contour interaction for high and low contrast optotypes in normal and amblyopic observers,” Ophthalmic Physiol. Opt. 19, 253–260 (1999).
    [CrossRef]
  18. R. F. Hess, S. C. Dakin, N. Kapoor, “The foveal ‘crowding’ effect: physics or physiology?” Vision Res. 40, 365–370 (2000).
    [CrossRef]
  19. R. F. Hess, C. B. Williams, A. Chaudhry, “Contour interaction for an easily resolvable stimulus,” J. Opt. Soc. Am. A 18, 2414–2418 (2001).
    [CrossRef]
  20. O. Ehrt, R. F. Hess, C. B. Williams, K. Sher, “Foveal contrast thresholds exhibit spatial-frequency- and polarity-specific contour interactions,” J. Opt. Soc. Am. A 20, 11–17 (2003).
    [CrossRef]
  21. H. Strasburger, “Invariance of the psychometric function for character recognition across the visual field,” Percept. Psychophys. 63, 1356–1376 (2001).
    [CrossRef]
  22. K. E. Higgins, A. Arditi, K. Knoblauch, “Detection and identification of mirror-image letter pairs in central and peripheral vision,” Vision Res. 36, 331–337 (1996).
    [CrossRef] [PubMed]
  23. F. A. Wichmann, N. J. Hill, “The psychometric function: I. Fitting, sampling, and goodness of fit,” Percept. Psychophys. 63, 1293–1313 (2001).
    [CrossRef]
  24. L. A. Olzak, J. P. Thomas, “Neural recoding in human pattern vision: model and mechanisms,” Vision Res. 39, 231–256 (1999).
    [CrossRef] [PubMed]
  25. J. P. Thomas, “Detection and identification: how are they related?” J. Opt. Soc. Am. A 2, 1457–1467 (1985).
    [CrossRef] [PubMed]
  26. J. P. Thomas, “Effect of eccentricity on the relationship between detection and identification,” J. Opt. Soc. Am. A 4, 1599–1605 (1987).
    [CrossRef] [PubMed]

2003 (2)

2002 (1)

D. M. Levi, S. A. Klein, S. Hariharan, “Suppressive and facilitatory spatial interactions in foveal vision: foveal crowding is simple contrast masking,” J. Vision 2, 140–166 (2002), p. 140.

2001 (4)

R. F. Hess, C. B. Williams, A. Chaudhry, “Contour interaction for an easily resolvable stimulus,” J. Opt. Soc. Am. A 18, 2414–2418 (2001).
[CrossRef]

S. T. L. Chung, D. M. Levi, G. E. Legge, “Spatial-frequency and contrast properties of crowding,” Vision Res. 41, 1833–1850 (2001).
[CrossRef] [PubMed]

H. Strasburger, “Invariance of the psychometric function for character recognition across the visual field,” Percept. Psychophys. 63, 1356–1376 (2001).
[CrossRef]

F. A. Wichmann, N. J. Hill, “The psychometric function: I. Fitting, sampling, and goodness of fit,” Percept. Psychophys. 63, 1293–1313 (2001).
[CrossRef]

2000 (1)

R. F. Hess, S. C. Dakin, N. Kapoor, “The foveal ‘crowding’ effect: physics or physiology?” Vision Res. 40, 365–370 (2000).
[CrossRef]

1999 (5)

A. J. Simmers, L. S. Gray, P. V. McGraw, B. Winn, “Contour interaction for high and low contrast optotypes in normal and amblyopic observers,” Ophthalmic Physiol. Opt. 19, 253–260 (1999).
[CrossRef]

J. A. Solomon, A. B. Watson, M. J. Morgan, “Transducer model produces facilitation from opposite-sign flanks,” Vision Res. 39, 987–992 (1999).
[CrossRef] [PubMed]

M. Palomares, M. C. LaPutt, D. G. Pelli, “Crowding is unlike masking,” Invest. Ophthalmol. Visual Sci. (Suppl.) 40, 351 (1999).

S. J. Leat, W. Li, K. Epp, “Crowding in central and eccentric vision: the effects of contour interaction and attention,” Invest. Ophthalmol. Visual Sci. 40, 504–512 (1999).

L. A. Olzak, J. P. Thomas, “Neural recoding in human pattern vision: model and mechanisms,” Vision Res. 39, 231–256 (1999).
[CrossRef] [PubMed]

1998 (1)

1996 (1)

K. E. Higgins, A. Arditi, K. Knoblauch, “Detection and identification of mirror-image letter pairs in central and peripheral vision,” Vision Res. 36, 331–337 (1996).
[CrossRef] [PubMed]

1993 (1)

U. Polat, D. Sagi, “Lateral interactions between spatial channels: suppression and facilitation revealed by lateral masking experiments,” Vision Res. 33, 993–999 (1993).
[CrossRef] [PubMed]

1992 (1)

A. Toet, D. M. Levi, “The two-dimensional shape of spatial interaction zones in the parafovea,” Vision Res. 32, 1349–1357 (1992).
[CrossRef] [PubMed]

1991 (1)

H. Strasburger, L. O. Harvey, I. Rentschler, “Contrast thresholds for identification of numeric characters in direct and eccentric view,” Percept. Psychophys. 49, 495–508 (1991).
[CrossRef] [PubMed]

1987 (1)

1985 (1)

1979 (1)

R. J. Jacobs, “Visual resolution and contour interaction in the fovea and periphery,” Vision Res. 19, 1187–1195 (1979).
[CrossRef] [PubMed]

1970 (1)

H. Bouma, “Interaction effects in parafoveal letter recognition,” Nature (London) 226, 177–178 (1970).
[CrossRef]

1963 (1)

1962 (1)

J. A. Stuart, H. M. Burian, “A study of separation difficulty: its relationship to visual acuity in normal and amblyopic eyes,” Am. J. Ophthalmol. 53, 471–477 (1962).
[PubMed]

1951 (1)

P. Müller, “Über das Sehen der Amblyopen,” Ophthalmologica 121, 143–149 (1951).
[CrossRef]

1923 (1)

W. Korte, “Über die Gestaltauffasssung im indirekten Sehen,” Z. Psychol. 93, 17–82 (1923).

Arditi, A.

K. E. Higgins, A. Arditi, K. Knoblauch, “Detection and identification of mirror-image letter pairs in central and peripheral vision,” Vision Res. 36, 331–337 (1996).
[CrossRef] [PubMed]

Bouma, H.

H. Bouma, “Interaction effects in parafoveal letter recognition,” Nature (London) 226, 177–178 (1970).
[CrossRef]

Burian, H. M.

J. A. Stuart, H. M. Burian, “A study of separation difficulty: its relationship to visual acuity in normal and amblyopic eyes,” Am. J. Ophthalmol. 53, 471–477 (1962).
[PubMed]

Chaudhry, A.

Chung, S. T. L.

S. T. L. Chung, D. M. Levi, G. E. Legge, “Spatial-frequency and contrast properties of crowding,” Vision Res. 41, 1833–1850 (2001).
[CrossRef] [PubMed]

Dakin, S. C.

R. F. Hess, S. C. Dakin, N. Kapoor, “The foveal ‘crowding’ effect: physics or physiology?” Vision Res. 40, 365–370 (2000).
[CrossRef]

Ehrt, O.

Epp, K.

S. J. Leat, W. Li, K. Epp, “Crowding in central and eccentric vision: the effects of contour interaction and attention,” Invest. Ophthalmol. Visual Sci. 40, 504–512 (1999).

Flom, M. C.

Gray, L. S.

A. J. Simmers, L. S. Gray, P. V. McGraw, B. Winn, “Contour interaction for high and low contrast optotypes in normal and amblyopic observers,” Ophthalmic Physiol. Opt. 19, 253–260 (1999).
[CrossRef]

Hariharan, S.

D. M. Levi, S. A. Klein, S. Hariharan, “Suppressive and facilitatory spatial interactions in foveal vision: foveal crowding is simple contrast masking,” J. Vision 2, 140–166 (2002), p. 140.

Harvey, L. O.

H. Strasburger, L. O. Harvey, I. Rentschler, “Contrast thresholds for identification of numeric characters in direct and eccentric view,” Percept. Psychophys. 49, 495–508 (1991).
[CrossRef] [PubMed]

Hess, R. F.

Higgins, K. E.

K. E. Higgins, A. Arditi, K. Knoblauch, “Detection and identification of mirror-image letter pairs in central and peripheral vision,” Vision Res. 36, 331–337 (1996).
[CrossRef] [PubMed]

Hill, N. J.

F. A. Wichmann, N. J. Hill, “The psychometric function: I. Fitting, sampling, and goodness of fit,” Percept. Psychophys. 63, 1293–1313 (2001).
[CrossRef]

Jacobs, R. J.

R. J. Jacobs, “Visual resolution and contour interaction in the fovea and periphery,” Vision Res. 19, 1187–1195 (1979).
[CrossRef] [PubMed]

Kahneman, D.

Kapoor, N.

R. F. Hess, S. C. Dakin, N. Kapoor, “The foveal ‘crowding’ effect: physics or physiology?” Vision Res. 40, 365–370 (2000).
[CrossRef]

Klein, S. A.

D. M. Levi, S. A. Klein, S. Hariharan, “Suppressive and facilitatory spatial interactions in foveal vision: foveal crowding is simple contrast masking,” J. Vision 2, 140–166 (2002), p. 140.

Knoblauch, K.

K. E. Higgins, A. Arditi, K. Knoblauch, “Detection and identification of mirror-image letter pairs in central and peripheral vision,” Vision Res. 36, 331–337 (1996).
[CrossRef] [PubMed]

Korte, W.

W. Korte, “Über die Gestaltauffasssung im indirekten Sehen,” Z. Psychol. 93, 17–82 (1923).

LaPutt, M. C.

M. Palomares, M. C. LaPutt, D. G. Pelli, “Crowding is unlike masking,” Invest. Ophthalmol. Visual Sci. (Suppl.) 40, 351 (1999).

Leat, S. J.

S. J. Leat, W. Li, K. Epp, “Crowding in central and eccentric vision: the effects of contour interaction and attention,” Invest. Ophthalmol. Visual Sci. 40, 504–512 (1999).

Legge, G. E.

S. T. L. Chung, D. M. Levi, G. E. Legge, “Spatial-frequency and contrast properties of crowding,” Vision Res. 41, 1833–1850 (2001).
[CrossRef] [PubMed]

Levi, D. M.

D. M. Levi, S. A. Klein, S. Hariharan, “Suppressive and facilitatory spatial interactions in foveal vision: foveal crowding is simple contrast masking,” J. Vision 2, 140–166 (2002), p. 140.

S. T. L. Chung, D. M. Levi, G. E. Legge, “Spatial-frequency and contrast properties of crowding,” Vision Res. 41, 1833–1850 (2001).
[CrossRef] [PubMed]

A. Toet, D. M. Levi, “The two-dimensional shape of spatial interaction zones in the parafovea,” Vision Res. 32, 1349–1357 (1992).
[CrossRef] [PubMed]

Li, W.

S. J. Leat, W. Li, K. Epp, “Crowding in central and eccentric vision: the effects of contour interaction and attention,” Invest. Ophthalmol. Visual Sci. 40, 504–512 (1999).

McGraw, P. V.

A. J. Simmers, L. S. Gray, P. V. McGraw, B. Winn, “Contour interaction for high and low contrast optotypes in normal and amblyopic observers,” Ophthalmic Physiol. Opt. 19, 253–260 (1999).
[CrossRef]

Morgan, M.

J. A. Solomon, M. Morgan, “Flanked targets: easier to see, harder to identify,” Perception (Suppl.) 32, 47 (2003).

Morgan, M. J.

J. A. Solomon, A. B. Watson, M. J. Morgan, “Transducer model produces facilitation from opposite-sign flanks,” Vision Res. 39, 987–992 (1999).
[CrossRef] [PubMed]

Müller, P.

P. Müller, “Über das Sehen der Amblyopen,” Ophthalmologica 121, 143–149 (1951).
[CrossRef]

Olzak, L. A.

L. A. Olzak, J. P. Thomas, “Neural recoding in human pattern vision: model and mechanisms,” Vision Res. 39, 231–256 (1999).
[CrossRef] [PubMed]

Palomares, M.

M. Palomares, M. C. LaPutt, D. G. Pelli, “Crowding is unlike masking,” Invest. Ophthalmol. Visual Sci. (Suppl.) 40, 351 (1999).

Pelli, D. G.

M. Palomares, M. C. LaPutt, D. G. Pelli, “Crowding is unlike masking,” Invest. Ophthalmol. Visual Sci. (Suppl.) 40, 351 (1999).

Polat, U.

U. Polat, D. Sagi, “Lateral interactions between spatial channels: suppression and facilitation revealed by lateral masking experiments,” Vision Res. 33, 993–999 (1993).
[CrossRef] [PubMed]

Rentschler, I.

H. Strasburger, L. O. Harvey, I. Rentschler, “Contrast thresholds for identification of numeric characters in direct and eccentric view,” Percept. Psychophys. 49, 495–508 (1991).
[CrossRef] [PubMed]

Sagi, D.

U. Polat, D. Sagi, “Lateral interactions between spatial channels: suppression and facilitation revealed by lateral masking experiments,” Vision Res. 33, 993–999 (1993).
[CrossRef] [PubMed]

Sher, K.

Simmers, A. J.

A. J. Simmers, L. S. Gray, P. V. McGraw, B. Winn, “Contour interaction for high and low contrast optotypes in normal and amblyopic observers,” Ophthalmic Physiol. Opt. 19, 253–260 (1999).
[CrossRef]

Solomon, J. A.

J. A. Solomon, M. Morgan, “Flanked targets: easier to see, harder to identify,” Perception (Suppl.) 32, 47 (2003).

J. A. Solomon, A. B. Watson, M. J. Morgan, “Transducer model produces facilitation from opposite-sign flanks,” Vision Res. 39, 987–992 (1999).
[CrossRef] [PubMed]

Strasburger, H.

H. Strasburger, “Invariance of the psychometric function for character recognition across the visual field,” Percept. Psychophys. 63, 1356–1376 (2001).
[CrossRef]

H. Strasburger, L. O. Harvey, I. Rentschler, “Contrast thresholds for identification of numeric characters in direct and eccentric view,” Percept. Psychophys. 49, 495–508 (1991).
[CrossRef] [PubMed]

Stuart, J. A.

J. A. Stuart, H. M. Burian, “A study of separation difficulty: its relationship to visual acuity in normal and amblyopic eyes,” Am. J. Ophthalmol. 53, 471–477 (1962).
[PubMed]

Thomas, J. P.

Toet, A.

A. Toet, D. M. Levi, “The two-dimensional shape of spatial interaction zones in the parafovea,” Vision Res. 32, 1349–1357 (1992).
[CrossRef] [PubMed]

Watson, A. B.

J. A. Solomon, A. B. Watson, M. J. Morgan, “Transducer model produces facilitation from opposite-sign flanks,” Vision Res. 39, 987–992 (1999).
[CrossRef] [PubMed]

Weymouth, F. W.

Wichmann, F. A.

F. A. Wichmann, N. J. Hill, “The psychometric function: I. Fitting, sampling, and goodness of fit,” Percept. Psychophys. 63, 1293–1313 (2001).
[CrossRef]

Williams, C. B.

Winn, B.

A. J. Simmers, L. S. Gray, P. V. McGraw, B. Winn, “Contour interaction for high and low contrast optotypes in normal and amblyopic observers,” Ophthalmic Physiol. Opt. 19, 253–260 (1999).
[CrossRef]

Am. J. Ophthalmol. (1)

J. A. Stuart, H. M. Burian, “A study of separation difficulty: its relationship to visual acuity in normal and amblyopic eyes,” Am. J. Ophthalmol. 53, 471–477 (1962).
[PubMed]

Invest. Ophthalmol. Visual Sci. (1)

S. J. Leat, W. Li, K. Epp, “Crowding in central and eccentric vision: the effects of contour interaction and attention,” Invest. Ophthalmol. Visual Sci. 40, 504–512 (1999).

Invest. Ophthalmol. Visual Sci. (Suppl.) (1)

M. Palomares, M. C. LaPutt, D. G. Pelli, “Crowding is unlike masking,” Invest. Ophthalmol. Visual Sci. (Suppl.) 40, 351 (1999).

J. Opt. Soc. Am. (1)

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

J. Vision (1)

D. M. Levi, S. A. Klein, S. Hariharan, “Suppressive and facilitatory spatial interactions in foveal vision: foveal crowding is simple contrast masking,” J. Vision 2, 140–166 (2002), p. 140.

Nature (London) (1)

H. Bouma, “Interaction effects in parafoveal letter recognition,” Nature (London) 226, 177–178 (1970).
[CrossRef]

Ophthalmic Physiol. Opt. (1)

A. J. Simmers, L. S. Gray, P. V. McGraw, B. Winn, “Contour interaction for high and low contrast optotypes in normal and amblyopic observers,” Ophthalmic Physiol. Opt. 19, 253–260 (1999).
[CrossRef]

Ophthalmologica (1)

P. Müller, “Über das Sehen der Amblyopen,” Ophthalmologica 121, 143–149 (1951).
[CrossRef]

Percept. Psychophys. (3)

H. Strasburger, L. O. Harvey, I. Rentschler, “Contrast thresholds for identification of numeric characters in direct and eccentric view,” Percept. Psychophys. 49, 495–508 (1991).
[CrossRef] [PubMed]

F. A. Wichmann, N. J. Hill, “The psychometric function: I. Fitting, sampling, and goodness of fit,” Percept. Psychophys. 63, 1293–1313 (2001).
[CrossRef]

H. Strasburger, “Invariance of the psychometric function for character recognition across the visual field,” Percept. Psychophys. 63, 1356–1376 (2001).
[CrossRef]

Perception (Suppl.) (1)

J. A. Solomon, M. Morgan, “Flanked targets: easier to see, harder to identify,” Perception (Suppl.) 32, 47 (2003).

Vision Res. (8)

R. J. Jacobs, “Visual resolution and contour interaction in the fovea and periphery,” Vision Res. 19, 1187–1195 (1979).
[CrossRef] [PubMed]

J. A. Solomon, A. B. Watson, M. J. Morgan, “Transducer model produces facilitation from opposite-sign flanks,” Vision Res. 39, 987–992 (1999).
[CrossRef] [PubMed]

U. Polat, D. Sagi, “Lateral interactions between spatial channels: suppression and facilitation revealed by lateral masking experiments,” Vision Res. 33, 993–999 (1993).
[CrossRef] [PubMed]

S. T. L. Chung, D. M. Levi, G. E. Legge, “Spatial-frequency and contrast properties of crowding,” Vision Res. 41, 1833–1850 (2001).
[CrossRef] [PubMed]

A. Toet, D. M. Levi, “The two-dimensional shape of spatial interaction zones in the parafovea,” Vision Res. 32, 1349–1357 (1992).
[CrossRef] [PubMed]

K. E. Higgins, A. Arditi, K. Knoblauch, “Detection and identification of mirror-image letter pairs in central and peripheral vision,” Vision Res. 36, 331–337 (1996).
[CrossRef] [PubMed]

L. A. Olzak, J. P. Thomas, “Neural recoding in human pattern vision: model and mechanisms,” Vision Res. 39, 231–256 (1999).
[CrossRef] [PubMed]

R. F. Hess, S. C. Dakin, N. Kapoor, “The foveal ‘crowding’ effect: physics or physiology?” Vision Res. 40, 365–370 (2000).
[CrossRef]

Z. Psychol. (1)

W. Korte, “Über die Gestaltauffasssung im indirekten Sehen,” Z. Psychol. 93, 17–82 (1923).

Cited By

OSA participates in CrossRef's Cited-By Linking service. Citing articles from OSA journals and other participating publishers are listed here.

Alert me when this article is cited.


Figures (4)

Fig. 1
Fig. 1

Sample stimulus with stroke width a and bar separation b. The contrast of the central Landolt C is suprathreshold for demonstration purposes.

Fig. 2
Fig. 2

Effect of (a)–(c) same-polarity bars and of (d)–(f) opposite-polarity bars on detection threshold (dashed curves) and discrimination threshold (solid curves) for different stimulus sizes: (a), (d) 0.25°; (b), (e) 0.5°; (c), (f) 1.0°. Contrast thresholds are plotted as a function of bar separation with the right end of each curve representing the unflanked condition. Each ordinate is scaled to fit the absolute threshold values, which increase with decreasing target size. Vertical bars represent the 95% confidence intervals. Analysis of variance for repeat measurements revealed whether there were any significant threshold changes; the associated p value is plotted to the right of each curve.

Fig. 3
Fig. 3

Total amount of foveal contour interaction calculated as the ratio of discrimination threshold with abutting bars to discrimination threshold without bars. Mean data of all five subjects are shown for same-polarity and opposite-polarity flanks at three target sizes. The vertical lines represent the 95% confidence intervals. The solid horizontal line represents no threshold elevation. T tests did not reveal any statistically significant difference between threshold elevation for same-polarity and opposite-polarity bars for any single target size.

Fig. 4
Fig. 4

Discrimination and detection data are summarized by plots of the ratio of discrimination threshold to detection threshold for different target sizes with (a) same-polarity and (b) opposite-polarity flanks. Vertical lines show the 95% confidence intervals for abutting and absent bars. For clarity of the figure the confidence intervals for intermediate bar separations have been omitted. The p values were calculated by analysis of variance for repeated measurements.

Metrics