Cognitive control of saccadic eye movements

Brain and Cognition

Volumn 68, Issue 3, 2008, Pages 327-340

  Hutton, S B ^a  

^a UNIVERSITY OF SUSSEX   (United Kingdom)

Author keywords

Antisaccades; Attention; Cognitive control; Inhibition; Prosaccades; Working memory

Indexed keywords

ARTICLE; ATTENTION; BEHAVIOR; COGNITION; HUMAN; LEARNING; MEDICAL LITERATURE; MEDICAL RESEARCH; PRIORITY JOURNAL; SACCADIC EYE MOVEMENT; WORKING MEMORY;

ATTENTION; COGNITION; EYE MOVEMENTS; HUMANS; MEMORY; MOTION PERCEPTION; PSYCHOMOTOR PERFORMANCE; REACTION TIME; SACCADES; VISUAL PERCEPTION;

EID: 56349117149     PISSN: 02782626     EISSN: 10902147     Source Type: Journal    
DOI: 10.1016/j.bandc.2008.08.021     Document Type: Article

References (136)

1. Akdal G., Hodgson T.L., Hill A.C., Mannan S., and Kennard C. Visual object memory and memory-guided saccades rely on shared mental representations. Experimental Brain Research 143 (2002) 509-514
2. Awh E., and Jonides J. Overlapping mechanisms of attention and spatial working memory. Trends in Cognitive Science 5 (2001) 119-126
3. Awh E., Jonides J., and Reuter-Lorenz P.A. Rehearsal in spatial working memory. Journal of Experimental Psychology Human Perception and Performance 24 (1998) 780-790
4. Baddeley A. Working memory, thought and action (2007), Oxford University Press, USA
5. Baddeley A., and Della Sala S. Working memory and executive control. Philosophical transactions of the Royal Society of London Series B Biological Sciences 351 (1996) 1397-1403
6. Baldauf D., and Deubel H. Properties of attentional selection during the preparation of sequential saccades. Experimental Brain Research 11 (2007) Epub. ahead of print
7. Beauchamp M.S., Petit L., Ellmore T.M., Ingeholm J., and Haxby J.V. A parametric fMRI study of overt and covert shifts of visuospatial attention. Neuroimage 14 (2001) 310-321
8. Becker W., and Fuchs A.F. Further properties of the human saccadic system: Eye movements and correction saccades with and with-out visual fixation points. Vision Research 9 (1969) 1247-1258
9. Blaukopf C.L., and DiGirolamo G.J. Differential effects of reward and punishment on conscious and unconscious eye movements. Experimental Brain Research 174 (2006) 786-792
10. Botvinick M.M., Braver T.S., Barch D.M., Carter C.S., and Cohen J.D. Conflict monitoring and cognitive control. Psychological Review 108 (2001) 624-652
11. Bronstein A.M., and Kennard C. Predictive eye saccades are different from visually triggered saccades. Vision Research 27 (1987) 517-520
12. Bunge S.A., Ochsner K.N., Desmond J.E., Glover G.H., and Gabrieli J.D. Prefrontal regions involved in keeping information in and out of mind. Brain 124 (2001) 2074-2086
13. Carpenter R.H.S. Oculomotor procrastination. In: Fisher D.F., Monty R.A., and Senders J.W. (Eds). Eye movements: Cognition and visual perception (1981), Lawrence Erlbaum, Hillsdale 237-246
14. Carpenter R.H.S. Choosing where to look. Current Biology 4 (1994) 341-343
15. Carpenter R.H.S. Express saccades: Is bimodality a result of the order of stimulus presentation?. Vision Research 41 (2001) 1145-1151
16. Carpenter R.H.S., and Williams M.L.L. Neural computation of log likelihood in the control of saccadic eye movements. Nature 377 (1995) 59-62
17. Cavegn D. Bilateral interactions in saccade programming. A saccade-latency study. Experimental Brain Research 109 (1996) 312-332
18. Clark J.J. Spatial attention and latencies of saccadic eye movements. Vision Research 39 (1999) 585-602
19. Craig G.L., Stelmach L.B., and Tam W.J. Control' of reflexive and voluntary saccades in the gap effect. Perception & psychophysics 61 (1999) 935-942
20. Crawford T.J., Bennett D., Lekwuwa G., Shaunak S., and Deakin J.F. Cognition and the inhibitory control of saccades in schizophrenia and Parkinson's disease. Progress in Brain Research 140 (2002) 449-466
21. Crawford T.J., Haeger B., Kennard C., Reveley M.A., and Henderson L. Saccadic abnormalities in psychotic patients. I. Neuroleptic-free psychotic patients. Psychological Medicine 25 (1995) 461-471
22. Cutsuridis V., Smyrnis N., Evdokimidis I., and Perantonis S. A neural model of decision-making by the superior colicullus in an antisaccade task. Neural Networks 20 (2007) 690-704
23. Deubel H., and Schneider W.X. Saccade target selection and object recognition: Evidence for a common attentional mechanism. Vision Research 36 (1996) 1827-1837
24. Dick S., Kathmann N., Ostendorf F., and Ploner C.J. Differential effects of target probability on saccade latencies in gap and warning tasks. Experimental Brain Research 164 (2005) 458-463
25. Dickov L.A., and Morrison J.D. Effects of uncertainty and target displacement on the latency of express saccades in man. Vision Research 46 (2006) 2505-2512
26. Doyle M., and Walker R. Curved saccade trajectories: Voluntary and reflexive saccades curve away from irrelevant distractors. Experimental Brain Research 139 (2001) 333-344
27. Duka T., and Lupp A. The effects of incentive on antisaccades: Is a dopaminergic mechanism involved?. Behavioural Pharmacology 8 (1997) 373-382
28. Dyckman K.A., and McDowell J.E. Behavioral plasticity of antisaccade performance following daily practice. Experimental Brain Research 162 (2005) 63-69
29. Edelman J.A., Kristjánsson A., and Nakayama K. The influence of object-relative visuomotor set on express saccades. Journal of Vision 7 (2007) 12
30. Eenshuistra R.M., Ridderinkhof K.R., and van der Molen M.W. Age-related changes in antisaccade task performance: Inhibitory control or working-memory engagement?. Brain and Cognition 56 (2004) 177-188
31. Ettinger U., Kumari V., Crawford T.J., Davis R.E., Sharma T., Corr P.J., et al. Reliability of smooth pursuit, fixation, and saccadic eye movements. Psychophysiology 40 (2003) 620-628
32. Ettinger U., Kumari V., Zachariah E., Galea A., Crawford T.J., Corr P.J., et al. Effects of procyclidine on eye movements in schizophrenia. Neuropsychopharmacology 28 (2003) 2199-2208
33. Evdokimidis I., Smyrnis N., Constantinidis T.S., Stefanis N.C., Avramopoulos D., Paximadis C., et al. The antisaccade task in a sample of 2006 young men-I. Normal population characteristics. Experimental Brain Research 147 (2002) 45-52
34. Everling S., and Fischer B. The antisaccade: A review of basic research and clinical studies. Neuropsychologia 36 (1998) 885-899
35. Findlay J.M. Global visual processing for saccadic eye movements. Vision Research 22 (1982) 1033-1045
36. Findlay J.M., and Walker R. A model of saccade generation based on parallel processing and competitive inhibition. The Behavioral and Brain Sciences 22 (1999) 661-674
37. Fischer B., and Breitmeyer B. Mechanisms of visual attention revealed by saccadic eye movements. Neuropsychologia 25 (1987) 73-83
38. Fischer B., and Ramsperger E. Human express saccades: Extremely short reaction times of goal directed eye movements. Experimental Brain Research 57 (1984) 191-195
39. Fischer B., and Weber H. Characteristics of antisaccades in man. Experimental Brain Research 89 2 (1992) 415-424
40. Fischer B., and Weber H. Express saccades and visual-attention. Behavioral and Brain Sciences 16 3 (1993) 553-567
41. Fischer B., and Weber H. Effects of stimulus conditions on the performance of antisaccades in man. Experimental Brain Research 116 (1997) 191-200
42. Godijn R., and Kramer A.F. Prosaccades and antisaccades to onsets and color singletons: Evidence that erroneous prosaccades are not reflexive. Experimental Brain Research 172 (2006) 439-448
43. Godijn R., and Theeuwes J. Programming of endogenous and exogenous saccades: Evidence for a competitive integration model. Journal of Experimental Psychology Human Perception and Performance 28 (2002) 1039-1054
44. Godijn R., and Theeuwes J. Parallel allocation of attention prior to the execution of saccade sequences. Journal of Experimental Psychology Human Perception and Performance 29 (2003) 882-896
45. Guitton D., Buchtel H.A., and Douglas R.M. Frontal lobe lesions in man cause difficulties in suppressing reflexive glances and in generating goal-directed saccades. Experimental Brain Research 58 (1985) 455-472
46. Hallett P.E. Primary and secondary saccades to goals defined by instructions. Vision Research 18 (1978) 1279-1296
47. Hardin M.G., Schroth E., Pine D.S., and Ernst M. Incentive-related modulation of cognitive control in healthy, anxious, and depressed adolescents: Development and psychopathology related differences. Journal of Child Psychology and Psychiatry 48 (2007) 446-454
48. Hodgson T.L., Golding C., Molyva D., Rosenthal C.R., and Kennard C. Eye movements during task switching: Reflexive, symbolic, and affective contributions to response selection. Journal of Cognitive Neuroscience 16 (2004) 318-330
49. Hoffman J.E., and Subramaniam B. The role of visual attention in saccadic eye movements. Perception & psychophysics 57 (1995) 787-789
50. Hooge I.T., Over E.A., van Wezel R.J., and Frens M.A. Inhibition of return is not a foraging facilitator in saccadic search and free viewing. Vision Research 45 (2005) 1901-1908
51. Hunt A.R., and Kingstone A. Covert and overt voluntary attention: Linked or independent?. Cognitive Brain Research 18 (2003) 102-105
52. Hunt A.R., and Kingstone A. Inhibition of return: Dissociating attentional and oculomotor components. Journal of Experimental Psychology Human Perception and Performance 29 (2003) 1068-1074
53. Hutton S.B., Crawford T.J., Puri B.K., Duncan L.J., Chapman M., Kennard C., et al. Smooth pursuit and saccadic abnormalities in first-episode schizophrenia. Psychological Medicine 28 (1998) 685-692
54. Hutton S.B., Cuthbert I., Crawford T.J., Kennard C., Barnes T.R., Joyce E.M., et al. Saccadic hypometria in drug-naive and drug-treated schizophrenic patients: A working memory deficit?. Psychophysiology 38 (2001) 125-132
55. Hutton S.B., and Ettinger U. The antisaccade task as a research tool in psychopathology: A critical review. Psychophysiology 43 (2006) 302-313
56. Hutton S.B., Joyce E.M., Barnes T.R., and Kennard C. Saccadic distractibility in first-episode schizophrenia. Neuropsychologia 40 (2002) 1729-1736
57. Isotalo E., Lasker A.G., and Zee D.S. Cognitive influences on predictive saccadic tracking. Experimental Brain Research 165 (2005) 461-469
58. Jazbec S., Hardin M.G., Schroth E., McClure E., Pine D.S., Ernst M., et al. Age-related influence of contingencies on a saccade task. Experimental Brain Research 174 (2006) 754-762
59. Joiner W.M., and Shelhamer M. An internal clock generates repetitive predictive saccades. Experimental Brain Research 175 (2006) 305-320
60. Juan C.H., Shorter-Jacobi S.M., and Schall J.D. Dissociation of spatial attention and saccade preparation. Proceedings of the National Academy of Sciences of the United States of America 101 (2004) 15541-15544
61. Karoumi B., Ventre-Dominey J., Vighetto A., Dalery J., and d'Amato T. Saccadic eye movements in schizophrenic patients. Psychiatry Research 77 (1998) 9-19
62. Kimberg D.Y., and Farah M.J. Is there an inhibitory module in the prefrontal cortex? Working memory and the mechanisms underlying cognitive control. In: Monsell S., and Driver J. (Eds). Control of cognitive processes, attention and performance Vol. 18 (2001), MIT Press, Cambridge (MA)
63. Kingstone A., and Klein R.M. Visual offsets facilitate saccadic latency: Does predisengagement of visuospatial attention mediate this gap effect?. Journal of Experimental Psychology Human Perception and Performance 19 (1993) 1251-1265
64. Klein R.M. Does oculomotor readiness mediate cognitive control of visual attention?. In: Nickerson R. (Ed). Attention and performance Vol. 8 (1980), Erlbaum, Hillsdale
65. Klein R.M. Inhibition of return. Trends in Cognitive Science 4 (2000) 138-147
66. Klein C., Bruegner G., Foerster F., Mueller W., and Schweickhardt A. The gap effect in pro-saccades and anti-saccades in psychometric schizotypes. Biological Psychology 55 (2000) 25-39
67. Klein C., and Fischer B. Developmental fractionation and differential discrimination of the anti-saccadic direction error. Experimental Brain Research 165 (2005) 132-138
68. Klein C., and Foerster F. Development of pro- and antisaccade performance in participants aged 6 to 26 years. Psychophysiology 38 (2001) 179-190
69. Klein C., Raschke A., and Brandenbusch A. Development of pro- and antisaccades in children with attention-deficit hyperactivity disorder (ADHD) and healthy controls. Psychophysiology 40 (2003) 1-12
70. Koval M.J., Ford K.A., and Everling S. Effect of stimulus probability on anti-saccade error rates. Experimental Brain Research 159 (2004) 268-272
71. Kowler E., Anderson E., Dosher B., and Blaser E. The role of attention in the programming of saccades. Vision Research 35 (1995) 1897-1916
72. Krappmann P., Everling S., and Flohr H. Accuracy of visually and memory-guided antisaccades in man. Vision Research 38 (1998) 2979-2985
73. Kristjánsson A. Saccade landing point selection and the competition account of pro- and antisaccade generation: The involvement of visual attention--a review. Scandinavian Journal of Psychology 48 (2007) 97-113
74. Kristjánsson A., Chen Y., and Nakayama K. Less attention is more in the preparation of antisaccades, but not prosaccades. Nature Neuroscience 4 (2001) 1037-1042
75. Kristjánsson A., Vandenbroucke M.W., and Driver J. When pros become cons for anti- versus prosaccades: Factors with opposite or common effects on different saccade types. Experimental Brain Research 155 (2004) 231-244
76. Massen C. Parallel programming of exogenous and endogenous components in the antisaccade task. Quarterly Journal of Experimental Psychology A 57 (2004) 475-498
77. Mayr U. Conflict, consciousness, and control. Trends in Cognitive Science 8 (2004) 145-148
78. Mayr U., Awh E., and Laurey P. Conflict adaptation effects in the absence of executive control. Nat Neurosci. 6 (2003) 450-452
79. McSorley E., Haggard P., and Walker R. Time course of oculomotor inhibition revealed by saccade trajectory modulation. Journal of Neurophysiology 96 (2006) 1420-1424
80. Miller E.K., and Cohen J.D. An integrative theory of prefrontal cortex function. Annual Review of Neuroscience 24 (2001) 167-202
81. Milstein D.M., and Dorris M.C. The influence of expected value on saccadic preparation. The Journal of Neuroscience 27 (2007) 4810-4818
82. Mitchell J.P., Macrae C.N., and Gilchrist I.D. Working memory and the suppression of reflexive saccades. Journal of Cognitive Neuroscience 14 (2002) 95-103
83. Mokler A., and Fischer B. The recognition and correction of involuntary prosaccades in an antisaccade task. Experimental Brain Research 125 (1999) 511-516
84. Moschovakis A.K. The superior colliculus and eye movement control. Current Opinion in Neurobiology 6 (1996) 811-816
85. Mosimann U.P., Felblinger J., Colloby S.J., and Muri R.M. Verbal instructions and top-down saccade control. Experimental Brain Research 159 (2004) 263-267
86. Munoz D.P., and Everling S. Look away: The anti-saccade task and the voluntary control of eye movement. Nature Reviews Neuroscience 5 (2004) 218-228
87. Nieuwenhuis S., Broerse A., Nielen M.M.A., and de Jong R. A goal activation approach to the study of executive function: An application to antisaccade tasks. Brain and Cognition 56 2 (2004) 198-214
88. Nieuwenhuis S., Ridderinkhof K.R., Blom J., Band G.P.H., and Kok A. Error-related brain potentials are differentially related to awareness of response errors: Evidence from an antisaccade task. Psychophysiology 38 (2001) 752-760
89. Nobre A.C., Gitelman D.R., Dias E.C., and Mesulam M.M. Covert visual spatial orienting and saccades: Overlapping neural systems. Neuroimage 11 (2000) 210-216
90. Ohtsuka K., Sawa M., and Takeda M. Accuracy of memory-guided saccades. Ophthalmologica 198 (1989) 53-56
91. Olk B., and Kingstone A. Why are antisaccades slower than prosaccades? A novel finding using a new paradigm. Neuroreport 14 (2003) 151-155
92. O'Reilly R.C., Braver T.S., and Cohen J.D. A biologically-based neural network model of working memory. In: Shah P., and Miyake A. (Eds). Models of working memory (1999), Cambridge University Press
93. Ostendorf F., Finke C., and Ploner C.J. Inhibition of visual discrimination during a memory-guided saccade task. Journal of Neurophysiology 92 (2004) 660-664
94. O'Sullivan E.P., Shaunak S., Henderson L., Hawken M., Crawford T.J., Kennard C., et al. Abnormalities of predictive saccades in Parkinson's disease. Neuroreport 8 (1997) 1209-1213
95. Oswal A., Ogden M., and Carpenter R.H. The time course of stimulus expectation in a saccadic decision task. Journal of Neurophysiology 97 (2007) 2722-2730
96. Pare M., and Munoz D.P. Saccadic reaction time in the monkey: Advanced preparation of oculomotor programs is primarily responsible for express saccade occurrence. Journal of Neurophysiology 76 (1996) 3666-3681
97. Ploner C.J., Gaymard B., Rivaud S., Agid Y., and Pierrot-Deseilligny C. Temporal limits of spatial working memory in humans. The European Journal of Neuroscience 10 (1998) 794-797
98. Posner M.I. Orienting of attention. The Quarterly Journal of Experimental Psychology 3 (1980) 3-25
99. Posner M.I., and Cohen Y. Components of visual orienting. In: Bouma H., and Bouwhuis D. (Eds). Attention and performance Vol. 10 (1984), Erlbaum, Hillsdale, N.J.
100. Pratt J. Visual fixation offsets affect both the initiation and the kinematic features of saccades. Experimental Brain Research 118 (1998) 135-138
101. Pratt J., Lajonchere C.M., and Abrams R.A. Attentional modulation of the gap effect. Vision Research 46 (2006) 2602-2607
102. Rabbitt P. Errors and error correction in choice-response tasks. Journal of Experimental Psychology 71 (1966) 264-272
103. Rafal R.D., Calabresi P.A., Brennan C.W., and Sciolto T.K. Saccade preparation inhibits reorienting to recently attended locations. Journal of Experimental Psychology Human Perception and Performance 15 (1989) 673-685
104. Rayner K. Eye movements in reading and information processing: 20 years of research. Psychological Bulletin 124 (1998) 372-422
105. Remington R.W. Attention and saccadic eye movements. Journal of Experimental Psychology Human Perception and Performance 6 (1980) 726-744
106. Reuter B., and Kathmann N. Using saccade tasks as a tool to analyze executive dysfunctions in schizophrenia. Acta Psychologica 115 (2004) 255-269
107. Reuter B., Rakusan L., and Kathmann N. Poor antisaccade performance in schizophrenia: An inhibition deficit?. Psychiatry Research 135 (2005) 1-10
108. Reuter-Lorenz P.A., Hughes H.C., and Fendrich R. The reduction of saccadic latency by prior offset of the fixation point: An analysis of the gap effect. Perception & psychophysics 49 (1991) 167-175
109. Reuter-Lorenz P.A., Oonk H.M., Barnes L.L., and Hughes H.C. Effects of warning signals and fixation point offsets on the latencies of pro- versus antisaccades: Implications for an interpretation of the gap effect. Experimental Brain Research 103 (1995) 287-293
110. Rizzolatti G., Riggio L., Dascola I., and Umilta C. Re-orienting attention across the horizontal and vertical meridians: Evidence in favor of a premotor theory of attention. Neuropsychologia 25 (1987) 31-40
111. Rizzolatti G., Riggio L., and Sheliga B.M. Space and selective attention. In: Umilta C., and Moscovitch M. (Eds). Attention and performance conscious and nonconscious information processing Vol. 15 (1994), MIT Press, Cambridge, MA 231-265
112. Roberts R.J., Hager L.D., and Heron C. Prefrontal cognitive processes: Working memory and inhibition in the antisaccade task. Journal of Experimental Psychology: General 123 (1994) 374-393
113. Ross J., Burr D., and Morrone C. Suppression of the magnocellular pathway during saccades. Behavioural Brain Research 80 (1996) 1-8
114. Ross S.M., and Ross L.E. Children's and adults' predictive saccades to square-wave targets. Vision Research 27 (1987) 2177-2180
115. Rycroft N., Hutton S.B., and Rusted J.M. The antisaccade task as an index of sustained goal activation in working memory: Modulation by nicotine. Psychopharmacology 188 (2006) 521-529
116. Saslow M.G. Effecs of components of displacement-step stimuli upon latency o saccadic eye movement. Journal of the Optical Society of America 57 (1967) 1024-1029
117. Sato T.R., and Schall J.D. Effects of stimulus-response compatibility on neural selection in frontal eye field. Neuron 38 (2003) 637-648
118. Schall J.D. Neural basis of saccade target selection. Reviews in the Neurosciences 6 (1995) 63-85
119. Schneider W.X. VAM: A neuro-cognitive model for visual attention control of segmentation, object recognition, and space-based motor action. Visual Cognition 2 (1995) 331-375
120. Simo L.S., Krisky C.M., and Sweeney J.A. Functional neuroanatomy of anticipatory behavior: Dissociation between sensory-driven and memory-driven systems. Cerebral Cortex 15 (2005) 1982-1991
121. Smit A.C., Van Gisbergen J.A., and Cools A.R. A parametric analysis of human saccades in different experimental paradigms. Vision Research 27 (1987) 1745-1762
122. Smyrnis N., Evdokimidis I., Stefanis N.C., Constantinidis T.S., Avramopoulos D., Theleritis C., et al. The antisaccade task in a sample of 2006 young males-II. Effects of task parameters. Experimental Brain Research 147 (2002) 53-63
123. Smyrnis N., Malogiannis I.A., Evdokimidis I., Stefanis N.C., Theleritis C., Vaidakis A., et al. Attentional facilitation of response is impaired for antisaccades but not for saccades in patients with schizophrenia: Implications for cortical dysfunction. Experimental Brain Research 159 (2004) 47-54
124. Stark L., Vossius G., and Young L.R. Predictive control of eye tracking movements. IRE Transactions on Human Factors in Electronics HFE3 (1962) 52-57
125. Tatler B.W., and Hutton S.B. Trial by trial effects in the antisaccade task. Experimental Brain Research 179 (2007) 387-396
126. Taylor, A.G., Hutton, S. B. (in preparation). The effects of task instructions on pro and antisaccade performance. British Journal of Psychology.
127. Theeuwes J., Kramer A.F., Hahn S., and Irwin D.E. Our eyes do not always go where we want them to go: Capture of the eyes by new objects. Psychological Science 9 (1998) 379-385
128. Theeuwes J., Olivers C.N., and Chizk C.L. Remembering a location makes the eyes curve away. Psychological Science 16 (2005) 196-199
129. Trappenberg T.P., Dorris M.C., Munoz D.P., and Klein R.M. A model of saccade initiation based on the competitive integration of exogenous and endogenous signals in the superior colliculus. Journal of Cognitive Neuroscience 13 (2001) 256-271
130. Unsworth N., Schrock J.C., and Engle R.W. Working memory capacity and the antisaccade task: Individual differences in voluntary saccade control. Journal of Experimental Psychology: Learning, Memory, and Cognition 30 (2004) 1302-1321
131. van der Heijden A.H.C. Selective attention in vision (1992), Routledge, London
132. Walker R., Kentridge R., and Findlay J. Independent contributions of the orienting of attention, fixation offset and bilateral stimulation on human saccadic latencies. Experimental Brain Research 103 (1995) 294-310
133. Walker R., Walker D.G., Husain M., and Kennard C. Control of voluntary and reflexive saccades. Experimental Brain Research 130 (2000) 540-544
134. Weber H., Durr N., and Fischer B. Effects of pre-cues on voluntary and reflexive saccade generation. II. Pro-cues for anti-saccades. Experimental Brain Research 120 (1998) 417-431
135. Wenban-Smith M.G., and Findlay J.M. Express saccades: Is there a separate population in humans?. Experimental Brain Research 87 (1991) 218-222
136. White J.M., Sparks D.L., and Stanford T.R. Saccades to remembered target locations: an analysis of systematic and variable errors. Vision Research 34 (1994) 79-92