Saccades made to outline drawings of eccentric forms were compared with saccades made to single-point targets. Saccades could be directed to designated locations within eccentric forms nearly as accurately and precisely as they could be directed to single points. Saccades directed to the form as a whole landed at consistent locations near the center of the form. These results show that contour information is sufficient for accurate computation of a saccadic command and that this computation is constrained by the internal coding of the shape. A serial two-stage process, voluntary selection followed by a weighted-averaging process, is proposed for computation of the saccadic command based on information provided by shape.
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Comparisons of Saccades to Designated Locations within Forms with Saccades to Points for Subjects EK and PHa
Location
Saccadic Measures
Subject EK
Subject PH
90-deg Angle on the Right
90-deg Angle on the Left
90-deg Angle on the Right
Form
Points
Form
Points
Form
Points
A
Size (SD)
92.7 (9.3)
96.8 (10.4)
88.4 (5.7)
88.4 (10.5)
106.1 (10.3)
104.2 (7.4)
Error
−6.3
−2.2
7.4
7.4
7.1
5.2
Latency (SD)
279 (46)
334 (65)
243 (35)
268 (51)
262 (37)
272 (56)
N
33
47
41
67
47
42
B
Size (SD)
83.9 (10.0)
80.8 (10.5)
95.4 (11.4)
100.2 (13.5)
93.4 (8.4)
90.6 (7.2)
Error
2.9
−0.2
−3.6
1.2
12.4
9.6
Latency (SD)
265 (76)
303 (71)
277 (40)
309 (35)
254 (50)
291 (54)
N
55
69
43
50
56
59
C
Size (SD)
85.8 (9.4)
88.6 (8.9)
96.1 (8.2)
104.7 (9.7)
93.4 (8.9)
86.9 (5.9)
Error
4.8
7.6
−2.9
5.7
12.4
5.9
Latency (SD)
260 (69)
283 (80)
267 (63)
288 (40)
260 (39)
273 (40)
N
57
62
42
50
64
39
D
Size (SD)
95.4 (10.1)
96.5 (12.4)
86.6 (10.0)
85.2 (9.0)
102.1 (9.1)
104.5 (9.8)
Error
−3.6
−2.5
5.6
4.2
3.1
5.5
Latency (SD)
291 (68)
311 (85)
248 (55)
278 (46)
260 (46)
274 (55)
N
50
37
54
43
70
47
Location A is the symmetric point of the triangle, location B is the midpoint of the base, location C is aligned vertically with the symmetric point and horizontally with the midpoint of the base, location D is aligned vertically with the midpoint of the base and horizontally with the symmetric point. Perfectly accurate saccades to the two nearer locations would be 81 arcmin, to the two further locations would be 99 arcmin. Horizontal saccade sizes and errors (saccade size–target eccentricity) are shown in minutes of arc. Latencies are in milliseconds.
Table 2
Comparison of Saccades to Designated Locations within Forms with Saccades to Points for Subjects EK and PH When Subjects Were Under Instructions to Equate Saccadic Latencies for Form and Point Targetsa
Location
Saccadic Measures
Subject EK
Subject PH
90-deg Angle on the Left
90-deg Angle on the Right
Form
Points
Form
Points
A
Size (SD)
86.4 (8.1)
82.7 (8.1)
108.1 (9.1)
101.6 (8.8)
Error
1.7
5.4
9.1
2.6
Latency (SD)
290 (52)
321 (48)
279 (41)
287 (36)
N
40
80
58
51
B
Size (SD)
94.6 (9.9)
97.0 (6.8)
88.9 (8.6)
87.5 (7.6)
Error
−4.4
−2.0
7.9
6.5
Latency (SD)
340 (55)
362 (63)
263 (43)
273 (42)
N
48
57
66
49
C
Size (SD)
94.5 (10.2)
97.2 (7.8)
88.7 (7.4)
85.4 (7.0)
Error
−4.5
−1.8
7.7
4.4
Latency (SD)
329 (71)
345 (49)
263 (42)
272 (33)
N
48
46
62
42
D
Size (SD)
85.8 (7.0)
85.0 (6.6)
100.1 (11.4)
103.8 (7.9)
Error
4.8
4.0
1.1
4.8
Latency (SD)
297 (40)
329 (53)
298 (82)
294 (33)
N
66
78
56
41
Location A is the symmetric point of the triangle, location B is the midpoint of the base, location C is aligned vertically with the symmetric point horizontally with the midpoint of the base, location D is aligned vertically with and midpoint of the base and horizontally with the symmetric point. Perfectly accurate saccades to the two nearer locations would be 81 arcmin, to the two further locations would be 99 arcmin. Horizontal saccade sizes and errors (saccade size − target eccentricity) are shown in minutes of arc. Latencies are in milliseconds.
Tables (2)
Table 1
Comparisons of Saccades to Designated Locations within Forms with Saccades to Points for Subjects EK and PHa
Location
Saccadic Measures
Subject EK
Subject PH
90-deg Angle on the Right
90-deg Angle on the Left
90-deg Angle on the Right
Form
Points
Form
Points
Form
Points
A
Size (SD)
92.7 (9.3)
96.8 (10.4)
88.4 (5.7)
88.4 (10.5)
106.1 (10.3)
104.2 (7.4)
Error
−6.3
−2.2
7.4
7.4
7.1
5.2
Latency (SD)
279 (46)
334 (65)
243 (35)
268 (51)
262 (37)
272 (56)
N
33
47
41
67
47
42
B
Size (SD)
83.9 (10.0)
80.8 (10.5)
95.4 (11.4)
100.2 (13.5)
93.4 (8.4)
90.6 (7.2)
Error
2.9
−0.2
−3.6
1.2
12.4
9.6
Latency (SD)
265 (76)
303 (71)
277 (40)
309 (35)
254 (50)
291 (54)
N
55
69
43
50
56
59
C
Size (SD)
85.8 (9.4)
88.6 (8.9)
96.1 (8.2)
104.7 (9.7)
93.4 (8.9)
86.9 (5.9)
Error
4.8
7.6
−2.9
5.7
12.4
5.9
Latency (SD)
260 (69)
283 (80)
267 (63)
288 (40)
260 (39)
273 (40)
N
57
62
42
50
64
39
D
Size (SD)
95.4 (10.1)
96.5 (12.4)
86.6 (10.0)
85.2 (9.0)
102.1 (9.1)
104.5 (9.8)
Error
−3.6
−2.5
5.6
4.2
3.1
5.5
Latency (SD)
291 (68)
311 (85)
248 (55)
278 (46)
260 (46)
274 (55)
N
50
37
54
43
70
47
Location A is the symmetric point of the triangle, location B is the midpoint of the base, location C is aligned vertically with the symmetric point and horizontally with the midpoint of the base, location D is aligned vertically with the midpoint of the base and horizontally with the symmetric point. Perfectly accurate saccades to the two nearer locations would be 81 arcmin, to the two further locations would be 99 arcmin. Horizontal saccade sizes and errors (saccade size–target eccentricity) are shown in minutes of arc. Latencies are in milliseconds.
Table 2
Comparison of Saccades to Designated Locations within Forms with Saccades to Points for Subjects EK and PH When Subjects Were Under Instructions to Equate Saccadic Latencies for Form and Point Targetsa
Location
Saccadic Measures
Subject EK
Subject PH
90-deg Angle on the Left
90-deg Angle on the Right
Form
Points
Form
Points
A
Size (SD)
86.4 (8.1)
82.7 (8.1)
108.1 (9.1)
101.6 (8.8)
Error
1.7
5.4
9.1
2.6
Latency (SD)
290 (52)
321 (48)
279 (41)
287 (36)
N
40
80
58
51
B
Size (SD)
94.6 (9.9)
97.0 (6.8)
88.9 (8.6)
87.5 (7.6)
Error
−4.4
−2.0
7.9
6.5
Latency (SD)
340 (55)
362 (63)
263 (43)
273 (42)
N
48
57
66
49
C
Size (SD)
94.5 (10.2)
97.2 (7.8)
88.7 (7.4)
85.4 (7.0)
Error
−4.5
−1.8
7.7
4.4
Latency (SD)
329 (71)
345 (49)
263 (42)
272 (33)
N
48
46
62
42
D
Size (SD)
85.8 (7.0)
85.0 (6.6)
100.1 (11.4)
103.8 (7.9)
Error
4.8
4.0
1.1
4.8
Latency (SD)
297 (40)
329 (53)
298 (82)
294 (33)
N
66
78
56
41
Location A is the symmetric point of the triangle, location B is the midpoint of the base, location C is aligned vertically with the symmetric point horizontally with the midpoint of the base, location D is aligned vertically with and midpoint of the base and horizontally with the symmetric point. Perfectly accurate saccades to the two nearer locations would be 81 arcmin, to the two further locations would be 99 arcmin. Horizontal saccade sizes and errors (saccade size − target eccentricity) are shown in minutes of arc. Latencies are in milliseconds.
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