Fixation detection using a velocity threshold identification method
Source:R/fixation_VTI.R
fixation_VTI.RdDetermine fixations by assessing the velocity of eye-movements, using a method that is similar to that proposed by Salvucci & Goldberg (2000). Applies the algorithm used in VTI_saccade and removes the identified saccades before assessing whether separated fixations are outside of the dispersion tolerance. If they are outside of this tolerance, the fixation is treated as a new fixation regardless of the length of saccade separating them. Compared to fixation_dispersion(), fixation_VTI() is more conservative in determining a fixation as smaller saccades are discounted and the resulting data is treated as a continued fixation (assuming it is within the pixel tolerance set by disp_tol). Returns a summary of the fixations found per trial, including start and end coordinates, timing, duration, mean velocity, and peak velocity.
Usage
fixation_VTI(
data,
sample_rate = NULL,
threshold = 100,
min_dur = 150,
min_dur_sac = 20,
disp_tol = 100,
smooth = FALSE,
progress = TRUE
)Arguments
- data
A dataframe with raw data (time, x, y, trial) for one participant
- sample_rate
sample rate of the eye-tracker. If default of NULL, then it will be computed from the timestamp data and the number of samples
- threshold
velocity threshold (degrees of VA / sec) to be used for identifying saccades.
- min_dur
Minimum duration (in milliseconds) of period over which fixations are assessed
- min_dur_sac
Minimum duration (in milliseconds) for saccades to be determined
- disp_tol
Maximum tolerance (in pixels) for the dispersion of values allowed over fixation period
- smooth
include a call to eyetools::smoother on each trial
- progress
Display a progress bar
Value
a dataframe containing each detected fixation by trial, with mean x/y position in pixel, start and end times, and duration.
References
Salvucci, D. D., & Goldberg, J. H. (2000). Identifying fixations and saccades in eye-tracking protocols. Proceedings of the Symposium on Eye Tracking Research & Applications - ETRA '00, 71–78.
Examples
# \donttest{
data <- combine_eyes(HCL)
data <- interpolate(data)
fixation_VTI(data)
#> pID trialNumber fix_n start end duration x y min_dur
#> 1 118 1 1 0 177 177 960.6437 812.8221 150
#> 2 118 1 2 203 430 227 958.2697 583.3656 150
#> 3 118 1 3 447 747 300 960.3778 475.9596 150
#> 4 118 1 4 793 1183 390 541.9831 835.5657 150
#> 5 118 1 5 1220 1716 496 939.7497 501.3017 150
#> 6 118 1 6 1750 2190 440 964.8528 168.6481 150
#> 7 118 1 7 2246 2690 444 1538.0137 827.6809 150
#> 8 118 1 8 2753 3103 350 957.3398 405.5577 150
#> 9 118 1 9 3136 3676 540 945.4690 118.6267 150
#> 10 118 1 10 3739 4223 484 1517.4073 807.5911 150
#> 11 118 1 11 4283 4473 190 973.6412 337.0289 150
#> 12 118 1 12 4496 5343 847 963.7266 484.1273 150
#> 13 118 1 13 5393 6792 1399 510.3438 854.9526 150
#> 14 118 1 14 6826 6999 173 922.1760 641.0514 150
#> 15 118 1 15 7132 7602 470 967.1352 621.7611 150
#> 16 118 1 16 7642 8222 580 510.5671 825.6929 150
#> 17 118 1 17 8229 9292 1063 507.9624 858.4375 150
#> 18 118 1 18 9339 10062 723 939.2357 463.1219 150
#> 19 118 1 19 10092 10435 343 948.3431 128.4113 150
#> 20 118 1 20 10509 10702 193 552.3035 805.0026 150
#> 21 118 1 21 10745 11118 373 940.9351 461.8191 150
#> 22 118 1 22 11138 11905 767 951.2853 280.2861 150
#> 23 118 1 23 11928 12138 210 958.7384 430.9473 150
#> 24 118 1 24 12195 12678 483 1509.7039 823.3102 150
#> 25 118 1 25 12778 12972 194 1551.0203 843.0094 150
#> 26 118 1 26 13028 13461 433 950.6158 445.1187 150
#> 27 118 2 1 0 173 173 958.3036 777.7691 150
#> 28 118 2 2 193 366 173 970.6951 630.2603 150
#> 29 118 2 3 403 1146 743 1509.4951 814.5551 150
#> 30 118 2 4 1196 1426 230 949.9956 395.1318 150
#> 31 118 2 5 1449 1793 344 943.3226 146.2147 150
#> 32 118 2 6 1826 1989 163 941.2234 479.6616 150
#> 33 118 2 7 2029 2259 230 496.0487 813.4126 150
#> 34 118 2 8 2363 2623 260 490.8042 826.5507 150
#> 35 118 2 9 2686 3106 420 941.1481 173.0539 150
#> 36 118 2 10 3129 3542 413 954.5539 461.0351 150
#> 37 118 2 11 3562 3919 357 946.5559 180.6134 150
#> 38 118 2 12 3939 4266 327 937.1268 289.0324 150
#> 39 118 2 13 4286 5139 853 937.8746 208.3503 150
#> 40 118 2 14 5395 5765 370 503.1166 825.4203 150
#> 41 118 2 15 5892 6232 340 950.2006 156.7992 150
#> 42 118 2 16 6285 6749 464 478.0627 805.4038 150
#> 43 118 2 17 6795 7205 410 953.2971 473.3177 150
#> 44 118 2 18 7255 7632 377 1540.6049 809.6670 150
#> 45 118 3 1 0 223 223 NA NA 150
#> 46 118 3 2 403 683 280 962.6799 456.5565 150
#> 47 118 3 3 706 933 227 973.7131 177.9272 150
#> 48 118 3 4 986 1200 214 1501.2300 843.1251 150
#> 49 118 3 5 1260 1826 566 496.7830 834.2048 150
#> 50 118 3 6 1876 2270 394 949.8535 464.5749 150
#> 51 118 3 7 2290 2619 329 970.7820 184.9187 150
#> 52 118 3 8 2656 2993 337 952.1402 478.0073 150
#> 53 118 3 9 3039 3553 514 1519.2343 851.1845 150
#> 54 118 3 10 3586 3743 157 1005.1878 577.4765 150
#> 55 118 3 11 3873 4116 243 962.1855 470.8759 150
#> 56 118 3 12 4133 4543 410 947.0731 301.3392 150
#> 57 118 3 13 4566 4759 193 942.3187 442.7579 150
#> 58 118 3 14 4779 5263 484 951.4985 203.0580 150
#> 59 118 4 1 0 160 160 956.9020 813.5203 150
#> 60 118 4 2 196 540 344 1461.7599 801.0184 150
#> 61 118 4 3 583 913 330 991.8398 426.4369 150
#> 62 118 4 4 1123 1540 417 506.0490 841.5767 150
#> 63 118 4 5 1646 2386 740 1514.3155 847.2483 150
#> 64 118 4 6 2446 3349 903 526.3245 826.3137 150
#> 65 118 4 7 3403 3693 290 981.3899 439.3996 150
#> 66 118 4 8 3713 4156 443 959.1926 154.1393 150
#> 67 118 4 9 4216 4712 496 1477.7422 814.0045 150
#> 68 118 4 10 4816 5456 640 513.9902 844.9841 150
#> 69 118 4 11 5512 5839 327 924.2869 179.6302 150
#> 70 118 4 12 5859 6166 307 955.4995 474.4489 150
#> 71 118 4 13 6219 8009 1790 1529.4441 852.0016 150
#> 72 118 4 14 8072 8609 537 534.6695 898.9425 150
#> 73 118 4 15 8669 8915 246 1506.8455 866.1134 150
#> 74 118 4 16 8972 9182 210 942.4880 391.1045 150
#> 75 118 4 17 9199 9908 709 953.1363 269.1663 150
#> 76 118 5 1 193 436 243 640.6702 805.4574 150
#> 77 118 5 2 473 763 290 919.2050 450.3507 150
#> 78 118 5 3 1116 1663 547 1510.8790 843.1651 150
#> 79 118 5 4 1716 1966 250 981.2747 430.6643 150
#> 80 118 5 5 1986 2606 620 954.0395 247.1195 150
#> 81 118 5 6 2659 2996 337 1528.8691 795.0080 150
#> 82 118 5 7 3046 3682 636 954.2500 299.3152 150
#> 83 118 5 8 3739 3926 187 1514.7882 808.8336 150
#> 84 118 5 9 3979 4266 287 955.7087 160.9888 150
#> 85 118 6 1 0 173 173 967.6325 804.3820 150
#> 86 118 6 2 357 577 220 945.9536 433.1546 150
#> 87 118 6 3 637 1156 519 1508.3297 820.9397 150
#> 88 118 6 4 1216 1523 307 532.4881 812.5384 150
#> 89 118 6 5 1720 1966 246 942.3669 154.7100 150
#> 90 118 6 6 1996 2373 377 946.8854 468.3090 150
#> 91 118 6 7 2396 2823 427 947.6286 166.4201 150
#> 92 118 6 8 2846 3330 484 936.5148 443.4610 150
#> 93 118 6 9 3423 3759 336 1529.1296 807.1260 150
#> 94 118 6 10 3823 4286 463 493.8334 816.6065 150
#> 95 118 6 11 4329 4663 334 959.2445 504.8447 150
#> 96 118 6 12 4679 5206 527 953.1375 260.1750 150
#> 97 119 1 1 0 223 223 972.1103 765.7244 150
#> 98 119 1 2 240 419 179 937.0440 643.6233 150
#> 99 119 1 3 439 959 520 974.6348 419.9574 150
#> 100 119 1 4 1009 1386 377 409.2640 753.4045 150
#> 101 119 1 5 1589 1856 267 971.0424 304.7891 150
#> 102 119 1 6 1889 2066 177 979.2380 581.0955 150
#> 103 119 1 7 2112 3022 910 1500.3562 765.8028 150
#> 104 119 1 8 3089 3292 203 444.7179 735.7169 150
#> 105 119 1 9 3326 4159 833 964.2701 480.0865 150
#> 106 119 1 10 4209 4652 443 460.4234 761.3488 150
#> 107 119 1 11 4715 5005 290 1477.5086 754.9841 150
#> 108 119 1 12 5059 5272 213 439.7000 686.8906 150
#> 109 119 1 13 5278 6722 1444 412.1090 779.4104 150
#> 110 119 1 14 6741 7301 560 505.3288 727.6988 150
#> 111 119 1 15 7375 7598 223 1480.4473 767.7752 150
#> 112 119 1 16 7618 7885 267 1587.2292 743.6164 150
#> 113 119 1 17 7948 8448 500 995.6632 325.6133 150
#> 114 119 1 18 8498 8848 350 343.7616 673.5203 150
#> 115 119 1 19 8904 9108 204 970.3422 314.1502 150
#> 116 119 1 20 9154 9604 450 451.2965 775.9674 150
#> 117 119 1 21 9638 9814 176 890.3137 527.7975 150
#> 118 119 1 22 9828 9984 156 941.0363 462.3133 150
#> 119 119 2 1 0 160 160 964.4077 800.0306 150
#> 120 119 2 2 200 563 363 489.4246 748.2445 150
#> 121 119 2 3 626 783 157 1432.7215 766.1448 150
#> 122 119 2 4 800 1086 286 1546.5018 746.7085 150
#> 123 119 2 5 1273 1493 220 997.7612 399.4104 150
#> 124 119 2 6 1513 2086 573 950.6969 208.1089 150
#> 125 119 2 7 2106 2963 857 979.5507 414.6998 150
#> 126 119 2 8 3006 3216 210 934.7593 642.2169 150
#> 127 119 2 9 3249 3563 314 512.3586 766.2387 150
#> 128 119 2 10 3606 3996 390 958.9479 279.0520 150
#> 129 119 2 11 4026 4212 186 792.5927 449.8534 150
#> 130 119 2 12 4256 4462 206 518.6455 786.5630 150
#> 131 119 2 13 4526 5066 540 1472.5263 764.4450 150
#> 132 119 3 1 0 184 184 985.9541 730.5059 150
#> 133 119 3 2 220 663 443 472.1210 752.5903 150
#> 134 119 3 3 730 1157 427 1464.3207 712.1701 150
#> 135 119 3 4 1207 1643 436 968.3952 420.4352 150
#> 136 119 3 5 1670 2093 423 987.8821 119.0672 150
#> 137 119 3 6 2413 3110 697 1516.4018 753.7404 150
#> 138 119 3 7 3180 3926 746 446.9097 755.2470 150
#> 139 119 3 8 3993 4749 756 1499.2257 763.7347 150
#> 140 119 3 9 4766 4989 223 1389.2216 699.5839 150
#> 141 119 3 10 5086 5689 603 400.2932 714.6202 150
#> 142 119 3 11 5746 6782 1036 981.1028 436.1339 150
#> 143 119 3 12 6802 7135 333 965.8765 299.7169 150
#> 144 119 3 13 7405 7569 164 480.4713 776.6188 150
#> 145 119 4 1 0 233 233 975.1394 746.1660 150
#> 146 119 4 2 270 1217 947 427.4524 747.2374 150
#> 147 119 4 3 1446 1850 404 1443.5337 745.5802 150
#> 148 119 4 4 1956 2523 567 537.5963 766.5012 150
#> 149 119 4 5 2546 2993 447 394.9710 748.7150 150
#> 150 119 4 6 3039 3256 217 907.8480 480.2590 150
#> 151 119 4 7 3296 4143 847 489.1409 746.8854 150
#> 152 119 4 8 4206 5416 1210 1455.0079 710.4423 150
#> 153 119 4 9 5479 6062 583 482.7405 764.8192 150
#> 154 119 4 10 6232 6622 390 1527.8785 738.6195 150
#> 155 119 4 11 6689 7355 666 450.4148 774.5962 150
#> 156 119 4 12 7559 7749 190 965.3538 383.7982 150
#> 157 119 4 13 7769 8182 413 969.9331 144.8225 150
#> 158 119 4 14 8228 8602 374 950.3255 536.0833 150
#> 159 119 4 15 8635 9052 417 959.0249 284.1379 150
#> 160 119 5 1 0 210 210 976.5170 750.1115 150
#> 161 119 5 2 250 477 227 492.1806 735.4280 150
#> 162 119 5 3 497 917 420 371.6881 770.6937 150
#> 163 119 5 4 937 1097 160 506.1086 783.0628 150
#> 164 119 5 5 1167 2033 866 1490.6202 762.1272 150
#> 165 119 5 6 2143 2720 577 1608.9363 777.1772 150
#> 166 119 5 7 2883 3386 503 456.9285 766.7936 150
#> 167 119 5 8 3456 3989 533 1515.0700 747.5654 150
#> 168 119 5 9 4009 4499 490 1430.7991 767.7693 150
#> 169 119 5 10 4569 4826 257 494.2187 762.7068 150
#> 170 119 5 11 4846 5283 437 348.8281 779.3330 150
#> 171 119 5 12 5306 5516 210 524.1386 751.4163 150
#> 172 119 5 13 5596 6599 1003 1503.1187 779.2121 150
#> 173 119 5 14 6686 7395 709 523.7418 762.9001 150
#> 174 119 5 15 7439 8212 773 966.2146 417.9438 150
#> 175 119 5 16 8239 9009 770 977.0369 149.6783 150
#> 176 119 5 17 9085 9562 477 471.5830 707.7810 150
#> 177 119 5 18 9605 10148 543 958.2060 327.6902 150
#> 178 119 5 19 10168 10425 257 980.4097 178.6096 150
#> 179 119 5 20 10625 11755 1130 392.2884 759.8224 150
#> 180 119 5 21 11801 12374 573 929.6616 319.2279 150
#> 181 119 5 22 12618 12834 216 352.4790 822.6459 150
#> 182 119 6 1 0 236 236 963.4609 755.3811 150
#> 183 119 6 2 256 430 174 962.7514 619.0616 150
#> 184 119 6 3 626 2263 1637 413.3652 790.0949 150
#> 185 119 6 4 2283 2433 150 592.6529 756.9108 150
#> 186 119 6 5 2453 3049 596 468.5629 739.4379 150
#> 187 119 6 6 3179 4086 907 1534.3101 784.0435 150
#> 188 119 6 7 4266 4605 339 991.8175 481.4887 150
#> 189 119 6 8 4672 5245 573 950.9352 199.0034 150
#> 190 119 6 9 5272 6778 1506 980.3947 430.5640 150
#> 191 119 6 10 6882 7558 676 1586.7961 735.2838 150
#> 192 119 6 11 7605 7828 223 1043.5969 359.9672 150
#> 193 119 6 12 7848 9161 1313 952.2730 181.9225 150
#> 194 119 6 13 9181 9361 180 948.9465 266.7840 150
#> 195 119 6 14 9425 10081 656 1535.9884 741.0666 150
#> 196 119 6 15 10104 10281 177 1418.5998 761.3546 150
#> 197 119 6 16 10348 11018 670 464.4767 786.1714 150
#> 198 119 6 17 11084 11278 194 1333.7384 779.3773 150
#> 199 119 6 18 11297 11581 284 1524.3373 751.4210 150
#> 200 119 6 19 11644 11994 350 440.0377 727.9646 150
#> 201 119 6 20 12067 12671 604 987.9853 309.9513 150
#> disp_tol
#> 1 100
#> 2 100
#> 3 100
#> 4 100
#> 5 100
#> 6 100
#> 7 100
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#> 201 100
# }