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,
threshold = 100,
min_dur = 150,
min_dur_sac = 20,
disp_tol = 100,
smooth = FALSE,
progress = TRUE
)Arguments
- data
A dataframe with raw data (pID, time, x, y, trial), the standardised raw data form for eyetools
- 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 4 783 1190 407 543.1279 834.5434 150
#> 5 118 1 5 1220 1730 510 939.8145 500.3046 150
#> 6 118 1 6 1753 2190 437 964.9265 168.6218 150
#> 7 118 1 7 2246 2686 440 1538.1665 827.9873 150
#> 8 118 1 8 2753 2916 163 966.5097 351.1727 150
#> 9 118 1 9 2933 3133 200 949.4499 449.1512 150
#> 10 118 1 10 3126 3676 550 945.8062 118.8186 150
#> 11 118 1 11 3736 4219 483 1517.4546 807.8438 150
#> 12 118 1 12 4283 4473 190 973.7590 337.2340 150
#> 13 118 1 13 4496 5373 877 962.4422 485.2484 150
#> 14 118 1 14 5343 6822 1479 512.2158 853.7036 150
#> 15 118 1 15 6812 6999 187 919.8259 641.8424 150
#> 16 118 1 16 7136 7596 460 966.9237 621.3341 150
#> 17 118 1 17 7646 8222 576 510.5845 825.7554 150
#> 18 118 1 18 8229 9289 1060 508.0056 858.4632 150
#> 19 118 1 19 9342 10059 717 939.2560 463.0083 150
#> 20 118 1 20 10095 10465 370 945.8363 131.5389 150
#> 21 118 1 21 10499 10699 200 552.2622 804.5069 150
#> 22 118 1 22 10749 11115 366 940.8964 462.0165 150
#> 23 118 1 23 11142 11902 760 951.3329 280.4016 150
#> 24 118 1 24 11928 12135 207 958.5555 430.8222 150
#> 25 118 1 25 12198 12968 770 1521.8775 829.2840 150
#> 26 118 1 26 13032 13431 399 951.5551 442.6154 150
#> 27 118 2 1 0 173 173 958.3036 777.7691 150
#> 28 118 2 2 193 380 187 974.5044 631.8866 150
#> 29 118 2 3 376 1196 820 1506.1300 812.5378 150
#> 30 118 2 4 1189 1426 237 950.4405 395.8372 150
#> 31 118 2 5 1449 1796 347 943.4877 146.6723 150
#> 32 118 2 6 1819 2009 190 935.8919 483.3098 150
#> 33 118 2 7 2029 2619 590 493.0987 820.6721 150
#> 34 118 2 8 2689 3102 413 941.2462 172.4029 150
#> 35 118 2 9 3132 3539 407 954.6329 461.6827 150
#> 36 118 2 10 3566 3919 353 946.3553 180.3700 150
#> 37 118 2 11 3939 4266 327 937.1356 289.0297 150
#> 38 118 2 12 4286 5136 850 937.7621 207.9633 150
#> 39 118 2 13 5399 5759 360 503.2766 825.4297 150
#> 40 118 2 14 5895 6229 334 948.9428 156.7683 150
#> 41 118 2 15 6289 6745 456 477.9152 805.5287 150
#> 42 118 2 16 6799 7202 403 953.1376 473.4159 150
#> 43 118 3 1 0 220 220 NA NA 150
#> 44 118 3 2 403 683 280 962.6799 456.5565 150
#> 45 118 3 3 706 933 227 973.7131 177.9272 150
#> 46 118 3 4 993 1200 207 1501.6394 843.7145 150
#> 47 118 3 5 1260 1826 566 496.7830 834.2048 150
#> 48 118 3 6 1876 2270 394 949.6194 464.7100 150
#> 49 118 3 7 2290 2619 329 970.7820 184.9187 150
#> 50 118 3 8 2656 2989 333 951.6396 477.7824 150
#> 51 118 3 9 3056 3553 497 1518.9085 851.4880 150
#> 52 118 3 10 3586 3743 157 1005.1878 577.4765 150
#> 53 118 3 11 3873 4113 240 962.3067 471.0581 150
#> 54 118 3 12 4133 4543 410 947.0560 301.5257 150
#> 55 118 3 13 4566 4759 193 942.4467 443.0341 150
#> 56 118 3 14 4779 5263 484 951.4985 203.0580 150
#> 57 118 4 1 0 160 160 956.9020 813.5203 150
#> 58 118 4 2 193 343 150 1406.2372 800.3531 150
#> 59 118 4 3 360 540 180 1507.5290 801.4327 150
#> 60 118 4 4 560 913 353 994.3665 428.3371 150
#> 61 118 4 5 1103 1536 433 506.2403 840.4780 150
#> 62 118 4 6 1650 2383 733 1514.6499 847.2079 150
#> 63 118 4 7 2450 3346 896 526.0427 826.3692 150
#> 64 118 4 8 3406 3689 283 981.7425 439.5356 150
#> 65 118 4 9 3716 4153 437 958.8945 153.7166 150
#> 66 118 4 10 4219 4709 490 1478.6775 814.2137 150
#> 67 118 4 11 4819 5452 633 513.9950 844.8581 150
#> 68 118 4 12 5516 5839 323 925.1128 179.0145 150
#> 69 118 4 13 5856 6166 310 955.6167 474.1818 150
#> 70 118 4 14 6216 8059 1843 1527.7158 852.0435 150
#> 71 118 4 15 8022 8609 587 539.4569 898.9155 150
#> 72 118 4 16 8642 8912 270 1502.5136 866.6847 150
#> 73 118 4 17 8975 9182 207 942.5158 390.7862 150
#> 74 118 4 18 9199 9712 513 949.4149 261.9195 150
#> 75 118 5 1 196 433 237 640.0432 805.7758 150
#> 76 118 5 2 476 783 307 918.5103 452.4816 150
#> 77 118 5 3 763 973 210 676.9740 803.1841 150
#> 78 118 5 4 1099 1659 560 1510.1178 843.3821 150
#> 79 118 5 5 1719 1959 240 981.3653 431.4367 150
#> 80 118 5 6 1986 2606 620 954.0925 247.7249 150
#> 81 118 5 7 2659 2992 333 1528.8640 795.0453 150
#> 82 118 5 8 3049 3679 630 954.3285 299.2864 150
#> 83 118 5 9 3742 3932 190 1513.6826 806.9528 150
#> 84 118 5 10 3972 4266 294 956.1005 161.4779 150
#> 85 118 6 1 0 173 173 967.6325 804.3820 150
#> 86 118 6 2 357 577 220 945.8363 433.1657 150
#> 87 118 6 3 633 1210 577 1502.6897 820.9648 150
#> 88 118 6 4 1167 1523 356 541.0264 812.6489 150
#> 89 118 6 5 1720 1970 250 942.4061 155.3532 150
#> 90 118 6 6 1986 2373 387 946.8782 467.5378 150
#> 91 118 6 7 2396 2823 427 947.6286 166.4201 150
#> 92 118 6 8 2836 3326 490 936.0810 443.3592 150
#> 93 118 6 9 3426 3756 330 1529.1779 807.2287 150
#> 94 118 6 10 3826 4283 457 493.4553 816.6774 150
#> 95 118 6 11 4333 4663 330 959.4518 504.3423 150
#> 96 118 6 12 4679 5159 480 953.6388 260.8693 150
#> 97 119 1 1 0 223 223 972.1103 765.7244 150
#> 98 119 1 2 240 419 179 936.9682 643.4583 150
#> 99 119 1 3 439 1006 567 971.1363 421.9248 150
#> 100 119 1 4 989 1406 417 412.8899 751.2055 150
#> 101 119 1 5 1399 1573 174 804.7938 509.7751 150
#> 102 119 1 6 1589 1856 267 971.0424 304.7891 150
#> 103 119 1 7 1889 2076 187 981.7317 582.0018 150
#> 104 119 1 8 2102 3026 924 1500.1104 765.8978 150
#> 105 119 1 9 3089 3296 207 445.5798 735.4684 150
#> 106 119 1 10 3316 4162 846 963.7025 480.1758 150
#> 107 119 1 11 4185 4659 474 462.4674 760.9068 150
#> 108 119 1 12 4705 5059 354 1466.6914 752.2349 150
#> 109 119 1 13 5198 7351 2153 438.1199 764.9565 150
#> 110 119 1 14 7371 7598 227 1480.2390 767.7494 150
#> 111 119 1 15 7618 7895 277 1585.6331 742.2156 150
#> 112 119 1 16 7941 8444 503 996.0639 325.5463 150
#> 113 119 1 17 8501 8851 350 343.2499 673.4041 150
#> 114 119 1 18 8888 9108 220 968.4899 314.5223 150
#> 115 119 1 19 9154 9601 447 451.1232 775.7702 150
#> 116 119 1 20 9641 9981 340 914.0899 497.4818 150
#> 117 119 2 1 0 160 160 964.4077 800.0306 150
#> 118 119 2 2 200 563 363 489.4246 748.2445 150
#> 119 119 2 3 626 783 157 1432.7215 766.1448 150
#> 120 119 2 4 800 1086 286 1546.5018 746.7085 150
#> 121 119 2 5 1273 1493 220 997.7612 399.4104 150
#> 122 119 2 6 1513 2086 573 950.6969 208.1089 150
#> 123 119 2 7 2106 2963 857 979.5058 415.4418 150
#> 124 119 2 8 3006 3216 210 934.7593 642.2169 150
#> 125 119 2 9 3249 3563 314 512.3586 766.2387 150
#> 126 119 2 10 3606 3996 390 959.0141 278.7691 150
#> 127 119 2 11 4026 4212 186 792.7098 450.0493 150
#> 128 119 2 12 4256 4462 206 518.6455 786.5630 150
#> 129 119 2 13 4526 5066 540 1472.5163 764.4277 150
#> 130 119 3 1 0 200 200 981.6611 730.4572 150
#> 131 119 3 2 194 717 523 481.2994 752.0970 150
#> 132 119 3 3 727 1167 440 1463.6185 711.6945 150
#> 133 119 3 4 1190 1650 460 968.9511 420.4636 150
#> 134 119 3 5 1670 2033 363 988.2300 123.7073 150
#> 135 119 3 6 2413 3106 693 1516.4708 753.9228 150
#> 136 119 3 7 3183 3923 740 446.6575 755.3015 150
#> 137 119 3 8 3996 4753 757 1499.3788 763.7812 150
#> 138 119 3 9 4763 5013 250 1386.0553 699.7711 150
#> 139 119 3 10 5086 5686 600 400.0376 714.8983 150
#> 140 119 3 11 5749 6782 1033 980.9620 436.1020 150
#> 141 119 3 12 6802 7132 330 966.1208 300.9559 150
#> 142 119 4 1 0 253 253 971.3683 746.0566 150
#> 143 119 4 2 270 1217 947 427.5659 747.1888 150
#> 144 119 4 3 1446 1873 427 1441.6189 745.8055 150
#> 145 119 4 4 1960 2523 563 537.3871 766.3947 150
#> 146 119 4 5 2546 3000 454 395.6776 748.1303 150
#> 147 119 4 6 3036 3253 217 908.1463 479.9049 150
#> 148 119 4 7 3299 4139 840 488.8203 746.7495 150
#> 149 119 4 8 4209 5412 1203 1455.0616 710.4195 150
#> 150 119 4 9 5482 6059 577 482.4678 764.8231 150
#> 151 119 4 10 6232 6619 387 1528.0690 738.6647 150
#> 152 119 4 11 6692 7352 660 450.2031 774.6959 150
#> 153 119 4 12 7559 7742 183 965.2065 383.8848 150
#> 154 119 4 13 7772 8178 406 969.9090 144.8427 150
#> 155 119 4 14 8232 8598 366 950.2556 536.2692 150
#> 156 119 5 1 0 210 210 976.5170 750.1115 150
#> 157 119 5 2 244 477 233 492.8740 735.6804 150
#> 158 119 5 3 497 917 420 371.6881 770.6937 150
#> 159 119 5 4 937 1103 166 508.2954 782.8994 150
#> 160 119 5 5 1100 2033 933 1486.8775 762.0913 150
#> 161 119 5 6 2143 2726 583 1607.9763 776.6748 150
#> 162 119 5 7 2886 3386 500 457.2755 767.4715 150
#> 163 119 5 8 3393 3989 596 1509.5685 747.9117 150
#> 164 119 5 9 4009 4496 487 1431.5261 767.8143 150
#> 165 119 5 10 4579 4826 247 493.5553 762.4451 150
#> 166 119 5 11 4846 5289 443 349.1937 779.2816 150
#> 167 119 5 12 5286 5513 227 521.5009 751.7369 150
#> 168 119 5 13 5599 6596 997 1502.7039 779.1490 150
#> 169 119 5 14 6689 7402 713 524.1221 763.3493 150
#> 170 119 5 15 7439 8209 770 966.2373 418.0393 150
#> 171 119 5 16 8242 9005 763 976.8946 150.0364 150
#> 172 119 5 17 9089 9562 473 471.4173 707.9541 150
#> 173 119 5 18 9598 10148 550 958.5243 327.3672 150
#> 174 119 5 19 10168 10425 257 980.3276 178.7893 150
#> 175 119 5 20 10595 11755 1160 392.8766 759.6779 150
#> 176 119 5 21 11761 12374 613 927.5780 321.4340 150
#> 177 119 6 1 0 236 236 963.4609 755.3811 150
#> 178 119 6 2 256 436 180 962.9117 617.2494 150
#> 179 119 6 3 626 2266 1640 413.3380 790.3672 150
#> 180 119 6 4 2276 2433 157 591.3804 756.9897 150
#> 181 119 6 5 2453 3049 596 468.5629 739.4379 150
#> 182 119 6 6 3179 4086 907 1534.3101 784.0435 150
#> 183 119 6 7 4269 4605 336 991.7024 481.1540 150
#> 184 119 6 8 4656 5245 589 950.8301 201.0391 150
#> 185 119 6 9 5269 6775 1506 980.3141 430.5043 150
#> 186 119 6 10 6885 7555 670 1586.3520 735.5883 150
#> 187 119 6 11 7608 7828 220 1043.4398 360.0337 150
#> 188 119 6 12 7848 9161 1313 952.2215 181.7543 150
#> 189 119 6 13 9181 9358 177 948.7052 266.9317 150
#> 190 119 6 14 9428 10088 660 1536.3246 741.4289 150
#> 191 119 6 15 10098 10278 180 1418.9720 760.8927 150
#> 192 119 6 16 10351 11014 663 464.2243 786.3815 150
#> 193 119 6 17 11088 11278 190 1333.9099 779.3765 150
#> 194 119 6 18 11297 11577 280 1524.7641 751.3519 150
#> 195 119 6 19 11647 11994 347 439.4383 728.0833 150
#> 196 119 6 20 12071 12534 463 988.9682 311.6586 150
#> disp_tol
#> 1 100
#> 2 100
#> 3 100
#> 4 100
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#> 196 100
# }