I have a great friend who also turns out to be my roommate in the university dorms. He reveres color red. The first time we met I was wearing a hoodie whose middle third was red while he wore a red coat. We began conversing and then he brings up the fact that we're both wearing red. I replied with a probabilistic question to initiate a collaboration, 'what are the chances that two people on this floor wear the same color?' He asked me quite quizzically what I meant by that. I told him that I meant was what are the chances that out of 40 people two of them will wear the same color. The answer I got was strange, 'No, I understood that. My question is, what do you mean by "the same color"?'
Sections
1. Introduction
At that moment I was considering whether I should drop this conversation and politely disengage, whether I should ask more questions, or whether I should change the rooms. Since it was unlikely that I will change the rooms I decided to inquire more on his perception of the mundane red. It was clear to me already that we saw the colors differently. What wasn't clear to me was whether he was incapable of differentiating colors or hypercapable of differentiating them. From here on now, I will refer to that friend as John.
At this point I had the following hypothesis:
H1: John can differentiate colors better than on average.
'Aren't both reds the same.' He gave me a look of suspicion and said no. 'What about those two greens?' 'Same.' 'Those two blues?' 'Same. And, by the way, you're wearing a dirty red and I am not.' I looked down and naïvely checked whether it was dirty; it was not. It meant for me that he was not teasing me, but being serious about it. I had to revise my hypothesis,
H1: John can differentiate color red better than on average.
Nevertheless, I was still befuddled by the fact that I was seeing the same shade of red while he saw a different one. I asked other people, they all agreed that it was the same shade of red.
So I found some evidence to support the H1. Barely an explanation, however, as to why he was hypersensitive about red. So I decided to drop this matter for the time being and think
more about the causes of his ability. 'Red is my favorite color,' he added before I switched the topic.
While living with him I had time to notice his obsession with red. I was working on my laptop, and because we share the same table, on his side he laid down his paper notebook and pen. The cover of the notebook was red within red while the pen was currant. 'Wait a minute, this is not red,' I was jesting him. 'Of course not, but its pretty close, the ink color is different than the plastic on the pen and closer to actual red,' John said while showing me the text in his notebook. "Actual red," what an interesting form of speech. I wondered about what can be his "actual red." 'Show me actual red!' I was very excited at that time; maybe it was just me, or maybe it was simply because I have read too much Oliver Sacks at that time. The matter still stood,
H2: John's 'actual red' does not exist physically.
Which, in other words, meant that his perception of red was influenced by top-down processes and he had an ideal prototype of red on which he relied to categorize other reds in the world based on the difference from that prototype (Minda & Smith, 2011). It was a bit of an oversimplification on my side because how would John even conceive an 'actual red' in the first place without output from his retina? I had, therefore, another framework to fall back on.
'Let me see.' He looked around the room but could not find anything. 'Oh, this. Its pretty close.' He showed me his red notebook. Pretty close red is not actual red.
'Have you ever seen "actual red"?' He thought for a bit and then said yes, 'my red coat.' I was seriously considering that he was messing with me, 'are you serious right now?'
'Yeah.' H2 was not supported. Once again, I just dropped the discussion about red for later so that I could focus on my assignment and think more about what could be going on.
2. Theory
Top-down processing is processing of information at higher-order cognitive functions that modulate lower-order functions (Goldstein, 2014; Breedlove & Watson, 2017). For example, if you read the word wind there are two possibilities, you either read it as a word that refers to the movement of air (/wɪnd/) or as a word that refers to the act of turning, twisting, or wrapping (/waɪnd/). As such, the knowledge you possess changes the way you perceive the word. However, top-down processing is more complex, it also refers to conscious control. As I've previously said, hypothesis 2 hints at top-down processing of the color red which was not supported.
On the other hand, bottom-up processing refers to the processing of information from sensory inputs that trigger higher-order processing (Goldstein, 2014; Breedlove & Watson, 2017). As such, it can be considered that bottom-up processing reaches consciousness in an already modified form. For instance, if you hear a very loud noise to your left you will turn your attention towards the direction of the incoming sound (known as reflexive attention) (Breedlove & Watson, 2017). It was clear to me that since there exists an 'actual red' then whatever formed that concept in John's mind must be due to bottom-up processes. It, therefore, might be the more likely case that John can differentiate more shades of red because of biophysical differences in his retina.
H3: John discriminates between more shades of red because of biophysical differences in his retina.
One explanation to John's color thresholds can be a shift in green color cone responses. This explanation has two advantages. First, it would decrease the amount of overlap between long (red) and medium (green) wave-length cones, therefore, leading to a superior discrimination of color red. On the other hand, it would increase overlap between short (blue) and medium (green) wave-length cones; thus, leading to an increased confusion during the discrimination of these two colors. So far, this explanation is most in-line with a priori observations.
Figure 1
Stockman & Sharpe (2000) Cone response and wavelength.
In university I had one class called Cognition: Sensation and Perception which I loved. As a final project for that class we had to do our own literature review on a topic of our choice related to the course. Then, based on that review, we had to come up with a hypothesis based on the literature and then devise a methodology to test that hypothesis. The hypothesis our team has come up with was that only the absolute threshold and difference threshold for color blue should change when the night light mode is turned on. Absolute threshold refers to the minimum intensity of the stimulus that can be just detected (Goldstein, 2014). On the other hand, difference threshold (also known as just noticeable difference) refers to the amount that the stimulus intensity should be changed for a difference to be noticed (Goldstein, 2014). I designed a Python app that measures at what luminance level the participant would not be able to notice a difference between the maximum luminance level of 255 on a digital screen for the three main colors, red, green, and blue. In other words, the app would test and output the luminance levels for the three base digital colors at which participants barely notice any difference. The app used the method of limits (also known as the staircase method) to determine that difference threshold (Cornsweet, 1962; Goldstein, 2014).
Figure 1
Python application testing for the difference threshold for color red
The code can be found on this GitHub page.
3. Test
One day, I caught John in the room studying so I gave him my app to test his vision. While he was struggling with differentiating blue, I scribbled down a more specific version of hypothesis number three. Always, hypothesis should precede testing in deductive studies. Of course, the app is not a perfect measurement tool for all shades of red, because some shades are not pure red, but rather contain a combination of other colors (blue and green in the case of computer screen). However, it does a fair job on luminance levels because lower luminance levels can be considered shades of red combined with shades of black.
H4: John's luminance difference threshold for color red will be greater than sample's average.
Here are John's results:
| Color | Experimental | Adjusted |
|---|---|---|
| Red | 215.8 | -3.8 |
| Green | 238 | 18.4 |
| Blue | 205 | -14.6 |
The adjusted column was calculated by taking the difference between each score and their average. This is necessary because color factor is a within-subjects factor and, therefore, liable to a participants personal differences in color perception. In other words, to control for extraneous variables, such as luminance sensitivity, or eyesight problems, each participants' average scores were individually substracted from their experimental scores.
To test whether there are, after all, any differences in John's perception of color red, I used JASP to perform a Student's One Sample T-test. Normally, one sample t-test is used to look for differences between sample's mean and a hypothesized population mean when the population standard deviation is not known. I used it to check whether the sample's mean is lower than John's single score. In other words, I am using John's score as the hypothesized population mean. The sample's adjusted mean of just noticeable differences for color red (M = -6.1, SD = 2.2) are significantly lower than John's adjusted just noticeable difference of color red (M = -3.8), t(49) = -7.3, p < 0.05, Cohen's d = -1.03.
That sounds like it, however, I remember that John had lower ability to discriminate between blue and green. Therefore, I assume that his adjusted scores of JND will be lower for green (H5) and blue (H6).
The sample's adjusted mean of just noticeable differences for color green (M = 18.04, SD = 2.1) are not significantly higher than John's adjusted just noticeable difference of color blue (M = 18.4), t(49) = -1.2, p > 0.05, Cohen's d = -0.17.
The sample's adjusted mean of just noticeable differences for color blue (M = -12, SD = 3.5) are significantly higher than John's adjusted just noticeable difference of color blue (M = -14.6), t(49) = 5.4, p < 0.05, Cohen's d = 0.75.
In other words, there is evidence to support that John's just noticeable difference of color red is better, and for color blue worse, than the sample's mean.
4. Discussion
All the previously enumerated findings point towards the possibility that John's medium wave-length cones are shifted towards lower wavelengths; thus, increasing overlap and confusion with shades of blue and decreasing them with color red. This, however, might not be the only explanation. Another possibility is that John's medium wavelength cones are genetically less responsive, which, in theory, might also decrease the overlap with long-wavelengths.
References
Breedlove, S. M., & Watson, N. V. (2017). Behavioral neuroscience (Eighth edition). Sinauer Associates, Inc., Publishers.
Cornsweet, T. N. (1962). The staircase-method in psychophysics. The American Journal of Psychology, 75(3), 485. https://doi.org/10.2307/1419876
Goldstein, E. B. (2014). Sensation and perception (Ninth edition). Wadsworth, Cengage Learning.
Minda, J. P., & Smith, J. D. (2011). Prototype models of categorization: Basic formulation, predictions, and limitations. In E. M. Pothos & A. J. Wills (Eds.), Formal Approaches in Categorization (1st ed., pp. 40–64). Cambridge University Press. https://doi.org/10.1017/CBO9780511921322.003