Tag Archives: David Hume

The Face on Mars

A great example of pareidolia


Via Relatively Interesting

Back in 1976, the Viking Orbiter 1 acquired some images of the Cydonia region of Mars as part of the search for a potential landing site for the Viking Lander 2.  One of the images included a shot of a region that looked remarkably similar to a face. The image was released to the public by the Jet Propulsion Laboratory as part of their public relations effort.

Here it is:


Shortly after the images were released, some people (mostly in lay literature) argued that the face was artificially created, and that this was concrete evidence for either past or present intelligence on Mars. The rock formation looked so similar to a face – how could it not have been designed by an intelligent architect?

Some believe the face was created by Martians, others say it is a tomb, or part of an ancient city. Others believe that NASA is involved in a conspiracy to cover up the true nature of the Face – all part of a secret space program (then why would they have released the picture in the first place?).

Mac Tonnies goes so far as to say that the Face is a “genuine scientific enigma”. After NASA released new images of the Face in 1998, he claims that the “experts either don’t understand the workings of their own instruments or else feel somehow threatened by the Face’s enduring mystery.” (you can check out his very centered site here)

“Scientific enigma”, the Face is not.

Introducing…. Pareidolia

Humans – all humans – have an innate ability to detect patterns out of seemingly random noise. This ability is particularly strong when it comes to faces. As David Hume once said, “There is an universal tendency among mankind to conceive all beings like themselves, and to transfer every object, those qualities, with which they are familiarly acquainted, and of which they are intimately conscious. We find human faces in the moon, armies in the clouds; and by a natural propensity, if not corrected by experience and reflection, ascribe malice or good will to everything, that hurts or pleases us.

This phenomenon – detecting something clear and distinct from an apparently obscure stimulus – is called “pareidolia“. Carl Sagan hypothesized that, as a survival technique, human beings are “hard-wired” from birth to identify the human face. This allows people to use only minimal details to recognize faces from a distance and in poor visibility but can also lead them to interpret random images or patterns of light and shade as being faces.


Pareidolia not only applies to the detection of faces, but also to the perception of religious imagery and themes. In 1978, a New Mexican woman found that the burn marks on her tortilla she had made appeared similar to the face of Jesus Christ. Thousands of people came to see the burnt tortilla. Do think that if Son of God wanted to be seen, he would appear on a tortilla? Or the Virgin Mary, on a grilled cheese sandwich? Wouldn’t they pick something a little more majestic?

Revisiting the Face on Mars

But first, let’s revisit the Face on Mars. Back in 1976, the imaging technology was inferior to today’s, and the resolution of the images was significantly lower. Even compared to 1998, the resolution of space images has increased dramatically. Let’s compare the Face from lowest to highest resolution:


The 1976 version sure does look like a face, and if you strain your eyes, you might still see a face in the 1998 version. But what about the 2001 version?  Not so much.

Let’s look even closer at the 2001 version, just to be sure . . .

MORE . . .

Debating Homeopathy Part I

by Steven Novella via Skepticblog

warning-homeopathy-not-medicineSix years ago I was asked to participate in a group debate over the legitimacy of homeopathy at the University of CT (there were six speakers, three on each side). This year I was asked to participate in another homeopathy debate at UCONN, but this time one-on-one with Andre Saine ND from the Canadian Academy of Homeopathy taking the pro-homeopathy side. (I will provide a link when the video is posted online.)

While the basic facts of homeopathy have not changed in the past six years, the details and some of the specific arguments of the homeopaths have evolved, so it was good to get updated on what they are saying today. In this post I will discuss some overall patterns in the logic used to defend homeopathy and then discuss the debate over plausibility. In tomorrow’s post I will then discuss the clinical evidence, with some final overall analysis.

Believers and Skeptics

As with the last debate, the audience this time was packed with homeopaths and homeopathy proponents. When I was introduced as the president of the New England Skeptical Society, in fact, laughter erupted from the audience. But that’s alright – I like a challenge. It did not surprise me that the audience, and my opponent, were unfamiliar with basic skeptical principles. Andre, in fact, used the word “skeptic” as a pejorative throughout his presentation.

medicine badThe difference in our two positions, in fact, can be summarized as follows: Andre Saine accepts a very low standard of scientific evidence (at least with homeopathy, but probably generally given that he is a naturopath), whereas I, skeptics, and the scientific community generally require a more rigorous standard.

The basic pattern of Andre’s talk was to quote from one of my articles on homeopathy declaring some negative statement about homeopathy, and then to counter that statement with a reference to scientific evidence. The problem is, his references were to low-grade preliminary evidence, and never to solid reproducible evidence.

That is one functional difference between skeptics and believers – the threshold at which they consider scientific evidence to be credible and compelling (there are many reasons behind that difference, but that is the end result).

I was asked what level of evidence I would find convincing, and that’s an easy question to answer because skeptics spend a great deal of time exploring that very question. In fact, I have discussed this in the context of many things, not just homeopathy.

For any scientific claim (regardless of plausibility) scientific evidence is considered well-established when it simultaneously (that’s critical) fulfills the following four criteria:

  1. Methodologically rigorous, properly blinded, and sufficiently powered studies that adequately define and control for the variables of interest (confirmed by surviving peer-review and post-publication analysis).
  2. Positive results that are statistically significant.
  3. A reasonable signal to noise ratio (clinically significant for medical studies, or generally well within our ability to confidently detect).
  4. Independently reproducible. No matter who repeats the experiment, the effect is reliably detected.

This pattern of compelling evidence does not exist for ESP, acupuncture, any form of energy medicine, cold fusion or free energy claims, nor homeopathy. You may get one or two of those things, but never all four together. You do hear many excuses (special pleading) for why such evidence does not exist, but never the evidence itself.

The reason for this is simple – when you set the threshold any lower, you end up prematurely accepting claims that turn out not to be true.


homeopathyThe less plausible, the more outrageous and unconventional a scientific claim, the more nitpicky and uncompromising we should be in applying the standards above. This follows a Bayesian logic – you are not beginning with a blank slate, as if we have no prior knowledge, but rather are starting with existing well-established science and then extending that knowledge further.

To clarify – if a new claim seems implausible it does not mean that it is a-priori not true. It simply means that the threshold of evidence required to conclude that it is probably true is higher.

Scottish philosopher David Hume sort of captured this idea over two centuries ago when he wrote:

No testimony is sufficient to establish a miracle, unless the testimony be of such a kind, that its falsehood would be more miraculous than the fact which it endeavors to establish.

I like to think of it this way: The evidence for any new claim that contradicts prior established scientific conclusions must be at least as robust as the prior evidence it would overturn. You can also ask the question – what is more likely, that the relevant scientific facts are wrong, or that the new claim is wrong?

What is more likely, that much of what we think we know about physics, chemistry, biology, physiology, and medicine is wrong, or that the claims of homeopathy are wrong? I think this is an easy one.

MORE . . . Debating Homeopathy Part I

• Debating Homeopathy Part II

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