Color names, color categories, and color-cued visual search: sometimes, color perception is not categorical

Abstract

The relation between colors and their names is a classic case study for investigating the Sapir-Whorf hypothesis that categorical perception is imposed on perception by language. Here, we investigate the Sapir-Whorf prediction that visual search for a green target presented among blue distractors (or vice versa) should be faster than search for a green target presented among distractors of a different color of green (or for a blue target among different blue distractors). A. L. Gilbert, T. Regier, P. Kay, and R. B. Ivry (2006) reported that this Sapir-Whorf effect is restricted to the right visual field (RVF), because the major brain language centers are in the left cerebral hemisphere. We found no categorical effect at the Green-Blue color boundary and no categorical effect restricted to the RVF. Scaling of perceived color differences by Maximum Likelihood Difference Scaling (MLDS) also showed no categorical effect, including no effect specific to the RVF. Two models fit the data: a color difference model based on MLDS and a standard opponent-colors model of color discrimination based on the spectral sensitivities of the cones. Neither of these models nor any of our data suggested categorical perception of colors at the Green-Blue boundary, in either visual field.

Fig. 1

Stimulus configurations: a, Experiments I and III; b, Experiments II and IV. For the RT experiments, the positions of the “odd” target stimulus varied randomly from trial to trial; for the MOA measurement of the Green|Blue boundary, the “odd” target stimulus was in position 2 (panel a) or 1 (panel b) on all trials. c, top-bottom arrangement in Experiment V, used with the observers from Experiment II; d, right-visual-field stimulus in Experiment V, used with the observers from Experiment IV. The numerals by the disks are for exposition, and the black lines around the targets in a and b are for clarity and none of these were present in the actual stimuli. The colors are not colorimetrically correct because they have been adjusted to show up well on the reader's media (computer screen or printout).

Fig. 2

RT results from Experiment I, on 15 observers. Black disks, LVF; white disks, RVF. Each pair of LVF, RVF curves is for a different observer. The displacement constant is 0.5 sec. That is, the lowermost observer's data in the left-hand panel are plotted at the correct RT value, and each of the other observers’ data are displaced upward for clarity, by an integral multiple of 0.75 sec. Black triangles: each observer's Green|Blue boundary, plotted at an arbitrary y-axis value to point at the position where the RT minimum was predicted to be * = co-author KMG; §=co-author AMB.

Fig. 3

Analyses of the results of Experiments I, II, and III. a, average data from Fig. 2, ± 1 s.e.m. Black triangle: the average Green|Blue boundary. Dashed line: the colors that were used in the statistical analysis of the local minima. b, The color at which the minimum of the best- fitting parabola occurred, as a function of the Green|Blue boundary. If the RT minimum occurred reliably at the Green|Blue boundary, the two measures would be equal and highly correlated (dashed line). Instead, they were uncorrelated (solid line) and the RT minimum was at a bluer color azimuth than the Green|Blue boundary. c. RT DIFFERENCE as a function of COLOR DIFFERENCE for Experiment I; see text for description of the axes units. The prediction from Gilbert et al. is that the minimum value should be RT DIFFERENCE = -0.024 sec. at COLOR DIFFERENCE = 0 (white disk), and that function should rise to RT DIFFERENCE = 0 for the conditions where both target and distractor are on the same side of zero (black curve). The average value of RT DIFFERENCE at COLOR DIFFERENCE = 0 is statistically significantly different from the prediction. d, e, f, Analysis of the results of Experiment II; g, h, I, analysis of the results of Experiment III. d, g, conventions as in a; e, h, conventions as in b; f, I, conventions as in c.

Fig. 4

Bargraph of RTs from Experiment I, combined for analysis as in Gilbert et al. The RVF was slightly but significantly slower than the LVF, but, unlike in Gilbet et al., the RT difference between the “within color categories” and the “beteen color cateogies” conditions is not statistically significantly greater in the RVF than in the LVF.

Fig. 5

RT results from Experiment II. Displacement parameter = 0.75 sec. §, co-author AMB; #, BUI. ⦰, KTN. Other conventions as in Fig. 2.

Fig. 6

Individual RT button-press reaction-time data from Exeriment III. Displacement parameter: 0.75 sec. Symbols: the same subjects as in Fig. 4. Other conventions as in Fig. 2.

Fig. 7

a–d RT data from four individual observers who served in both button-press RT and saccadic RT experiments. Subjects AMB, KTN, and BUI served in Experiments II and III; subject KMG served in Experiments III and IV. RT for the saccadic eye movements to one of 12 color samples (black disks) was reliably faster than for the button press of one of two response keys (white disks), and the shape of the RT function for each subject was similar across the two tasks. e, f: average saccadic RT data from Experiment IV. RT for the look-at-the-button task (black symbols) was reliably faster than for the look-at-the-button task (white symbols).

Fig. 8

Three observers’ data from Experiment IV. White symbols: RVF; black symbols: LVF; circles: look-at-target, dark surround; diamonds: look-at-target, light surround; triangles: left-right, dark surround; squares: left-right, light surround. Black triangles: Green|Blue boundaries. Displacement parameters for the three subjects were 0.0 (*: co-author KMG), 0.25 sec (†) and 0.35 sec (‡).

Fig. 9

Analyses of the data from Experiment IV. a, the fastest color as a function of the Green|Blue boundary; line conventions as in Fig 3b. These two quantities are unrelated to one another. b–e, RT DIFFERENCE as a function of COLOR DIFFERENCE. There is no clear tendency for the data to follow the black curve, so there is no obvious tendency for there to be a local minimum near -0.024 sec in the RT DIFFERENCE data.

Fig. 10

MLDS data and their fits to the RT data. a—c, data from the observers from Experiment II, using stimulus configuration from Fig. 1b. Black triangles, MOA Green|Blue boundaries a, squares, MLDS ψ data; b, diamonds, Δψ data derived from a; c, the reciprocal of the Δψ data (line) was fitted using Eq. 2 to the RT data of Experiment II (circles). . d-i, data from the observers from Experiment IV; red and black solid lines, RVF and LVF respectively; d-f, dark surrounding field; g-I, light surrounding field. d, g, squares, MLDS ψ data; solid lines, point-to-point data; e, h, diamonds, Δψ data; solid lines, point-to-point data; f, i, the reciprocals of the Δψ data (solid lines) were fitted to the RT data of Experiment IV using Eq. 2 (white circles, RVF; black circles, LVF). White triangles and dashed lines throughout, the predicted curves for the RVF, taken from the LVF data, but assuming a 0.024 sec. category effect at the Green|Blue boundary (panels f,i).

Fig. 11

Examples of possible results of an MLDS experiment. Only the curve in (a) shows categorical perception.

Figure 12

RT data from Fig. 8, pooled across LVF and RVF, compared to the predictions from the delta-Psy results of Experiment V, fitted from Eq. 2 using a least squares criterion. *: co-author KMG.

Fig. 13

a. Diagram of a situation where perception is categorical in that RT is extra-fast at the color boundary (the white disk falls below the red prediction curve at the color boundary value indicated by the black triangle), but the extra-fast RT is not the fastest RT in the experiment (the fastest is the color indicated by the white triangle). This situation is especially revealed by the errors of prediction (b) which show a prominent dip at the Green|Blue boundary (black triangle), but none at the minimum of the data set (white triangle).

Fig. 14

The RT data from Experiments I, II, and III (a–c) were fitted using Equations 3, 4. Green lines, L-M contribution; blue lines, S contribution; red lines, the full model. d–f, errors of prediction from Eq. 3 (red lines) and from the MLDS fits in the case of Experiment II (black line in e). Black triangles: the average Green|Blue boundaries; green arrow: the L-M contribution goes up to infinity at the tritan colors where L = M. The errors of prediction do not show a pronounced local minimum at the Green|Blue boundary.

Fig. 15

The average RT data from Experiment IV (left panels), fitted using Equations 3, 4. Right panels, errors of prediction from Eq. 3 (red lines) and the MLDS fits. Conventions as in Fig. 14.

Fig. A1

The chromaticities of the stimuli in these experiments. Throughout: gray diamonds, the stimuli used by Gilbert et al., taken from their specified RGB values using the software they specified (www.easyrgb.com); “G” and dotted line, the Green|Blue boundary of Gilbert et al.; dashed line, Green|Blue boundary from the method of constant stimuli in our experiments; white disks, calibrated chromaticities of the green and blue stimuli used in our RT experiments. black triangles: chromaticities of our gray surrounding fields. A, Experiment I, black dots, the intended chromaticities taken from the Munsell samples used by (Kay & Kempton, 1984); B, Experiment II. Black disks, calibrated chromaticities of the stimuli used in the MLDS experiment. C, Experiment III; D, Experiment IV. Black disks, calibrate chromaticities of the MLDS stimuli, D, L, the green|blue boundary for the dark and light surrounding fields, respectively.

Fig. A2

The effects of testing range on the estimated Green|Blue boundary. Black triangles, Method of Constant Stimuli. White triangles: the Method of Adjustment, using the two-stimulus method described in the text. The Method of Constant Stimuli produced clear variation in the measured boundary (**p<0.0005, in each case), whereas the MOA was more reliable (p>0.25 in each case). However, the tendency to follow the range was not perfect, as the slope = 1 hypothesis (dashed lines) is also rejected in each case.