Multi-Modal Monkey Memory

Recognizing someone you know is actually not a simple cognitive task – it requires you interpret the information you’re currently receiving through your senses, and then link back to a previously-formed conceptual representation you have of the individual in question. It’s especially difficult if you are acting cross-modally, for example matching someone’s voice to a photograph or vice versa.

Oh yeah, I remember him. He's the one with the high squeaky voice, isn't he? (photo credit: Joe Kegley)

Recently, two separate studies have shown that rhesus macaque monkeys (Macaca mulatta) are quite up to this challenge, reflecting that they possess a considerable degree of social memory and engage in complex conceptual thinking about other individuals.

French Pictures

In the first study1, published earlier this year in Proceedings of the National Academy of Sciences, a French research team headed by Julian Sliwa of the University of Lyon confirmed that rhesus macaques are able to spontaneously match the faces of known macaques and humans to their voices.

In their experiments, the research team gave six macaques a large number of tests in which they played short voice samples of known individuals (coos and grunts for other macaques, short French sentences and phrases for humans) and then measured how long the macaques spontaneously looked at cropped photographs of two known faces, only one of which matched the voice they had heard. The researchers statistically analyzed whether the macaques spent more time looking at specific photos after hearing the matching voice than they did after hearing a different voice, and found that the macaques did indeed stare significantly longer at a photo – whether of another macaque or a human – if the matching voice had been played first.

In reviewing individual performance, the researchers observed that five of six of the macaques displayed this effect overall, and that a greater number were better at recognizing photos that matched human voices than ones matching the voices of fellow macaques (the researchers noted that they were surprised at this finding, but pointed out that perhaps the explanation was that there were more useful auditory cues in the human speech samples than there were in the monkey coo vocalizations). Finally, the researchers found that five of the six monkeys showed preferences for specific faces, spending an especially long time looking at matching” photos of certain individuals – often a “neighbor” monkey or the researcher who was their main caregiver.

The researchers concluded that rhesus macaques can recognize individuals, linking together abbreviated visual and auditory perceptual cues (small, two-dimensional photos and short sound samples) to spontaneously identify other macaques and socially-relevant humans, and even to reflect the preference biases they have towards specific individuals.

At the Movies

The second study2, published last week in PLOS ONE, extended the findings to show that rhesus macaques can also recognize photos of other macaques whom they had seen during video clips, an additional challenge because specific features can be harder to identify in dynamic movies than in still images.

In this study, researchers led by Ikuma Adachi of the Yerkes National Primate Research Center began by training five macaques to watch brief silent video clips of familiar individuals before identifying which of five randomly placed photos represented the individual in the video. At first the macaques were allowed to continue to look at the last frame of the video before having to choose the correct photo, but in a second phase of the experiment the screen went black after the video was played, and the monkeys had to choose the correct photo after a time lag.

In each case the macaques became proficient at the task, even performing well after seeing videos taken from a novel perspective that was substantially different than the view in the training videos. Thus, their performance suggested that they were able to recognize specific features of known individuals as they appeared in dynamically-changing scenes in a range of videos, and then extract that information to identify those individuals later on in still images.

Next, the researchers repeated the testing, but this time they tweaked the conditions by playing a brief vocalization right after showing the last frame of the some of the videos – either a vocalization of the macaque in the video (the “congruent condition”) or of a different macaque (the “incongruent condition”). Only two of the macaques participated in this testing, as apparently the other three weren’t comfortable with working in the sound isolation booth necessary for this phase.

The researchers found that the macaques, who had never been trained to use vocalizations to guide their test responses, continued to be good at choosing the “correct” photo, but that when they made errors, they were statistically more likely than chance to pick the image of the vocalizing monkey, rather than the one in the video.

In other words, hearing the vocalizations systematically biased the macaques’ choice behavior, indicating that the voices may have activated visual representations of the vocalizing monkeys that occasionally superseded the impact of what had been seen in the video. Again, the macaques were demonstrating how they processed the information they used to recognize information cross-modally.

So, clearly “see no evil” is linked to “hear no evil” – perhaps we’ll see how “speak no evil” fits into the picture in a later post.


1Sliwa J, Duhamel JR, Pascalis O, & Wirth S (2011). Spontaneous voice-face identity matching by rhesus monkeys for familiar conspecifics and humans. Proceedings of the National Academy of Sciences of the United States of America, 108 (4), 1735-40 PMID: 21220340.

2Adachi, I., & Hampton, R. (2011). Rhesus Monkeys See Who They Hear: Spontaneous Cross-Modal Memory for Familiar Conspecifics PLoS ONE, 6 (8) DOI: 10.1371/journal.pone.0023345.

Birds Display Their Animal Magnetism

In today’s post, I’d like to talk about something that many animals can do, and that humans simply cannot. I’m not referring to flying, breathing through gills, spinning webs, or running at 70 miles an hour across the African Savanna. I don’t even mean echolocation or pheromone detection or electroreception or polarized light detection, although some of these may be topics for future posts.

No, today I’d like to focus on magnetoreception, or the ability to sense the Earth’s magnetic fields as a means of perceiving one’s direction or location.

Many animals are able to sense magnetic fields, including honeybees, fruit flies, sea turtles, newts, lobsters, salmon, sharks and even bacteria, but some of the more in-depth and interesting research has been centered around migratory birds’ ability to use the Earth’s magnetic fields as a navigational aid as they make their long journeys.

For some reason, I've always felt strangely drawn to the North... (photo from Wikipedia, credit: Thermos)

While there are many aspects of this phenomenon that are still a mystery to us, scientists currently believe that there are two primary biophysical pathways that may explain how birds are able to navigate using the Earth’s geomagnetic fields. These two pathways are currently believed to coexist and complement each other, even though they involve very different processes.1

No, it's simple: just take a left at Norway and then bear right at Finland ... you can't miss it. (photo from Wikipedia, credit: Ernst Vikne)

The first pathway involves the use of iron-based receptors (crystals of a mineral known as magnetite) in the upper beak that can receive and transmit signals of a magnetic field directly to the bird’s brain via a specific nerve (the trigeminal nerve); the second pathway involves the activation of proteins called cryptochromes in the bird’s retina that, after being exposed to blue light, are sensitive to magnetic fields, enabling retinal cells to convert magnetic signals into visual ones and to transmit these signals to a specific sensory processing region (known as Cluster N) within the area of the bird’s forebrain responsible for vision.2

This second pathway may actually enable the bird to create images based on the magnetism fields – in other words, to actually see the Earth’s magnetism and use it as a navigational aid during migration, even during the dark of night.

Aside from being this being pretty cool, what is one to make of this from the standpoint of comparative cognition? Do we chalk one up for the birds (and the honeybees, fruit flies, sea turtles, etc.) and concede that humans are rather lacking in an important cognitive area?

I can already hear the objections. How can you compare this to those characteristics that truly set humans apart from the rest of animals? This is simply a heightened sensory ability, kind of like good eyesight or a fine sense of smell, and not that significant from the standpoint of higher cognition.

This is a fair point and an understandable (if anthropocentric) way to look at it, but there are still a couple of things you may want to consider:

First, we shouldn’t be overly dismissive of the amount cognitive sophistication involved in the long distance navigational feats. Think about it: migratory birds are able to travel, day and night, in all kinds of weather conditions, over great distances – sometimes thousands of miles – with a level of precision beyond our reach until the advent of GPS systems (thank you, Garmin). This sort of navigation is no simple process, either, as sensory input from multiple sources must be assessed, weighted, properly prioritized, reconciled and synthesized, all on a dynamic basis and in an environment when cues are constantly changing.

Also, consider whether this is another area where we humans may be tempted to slant the playing field to our advantage. While it’s easy to imagine our downplaying the significance of magnetoreception from a cognitive standpoint (after all, I just did), remember that we have no trouble in justifying to ourselves why “non-cognitive” human features, such as opposable thumbs and bipedalism, ought to be considered as important factors in distinguishing our capabilities from those of other animals. The point is not to argue that opposable thumbs weren’t critical to our becoming highly sophisticated tool-makers and users (I assume they were), but rather to suggest that we should be as flexible in thinking about factors pertinent to animal cognitive abilities as we are to those pertinent to our own.

Anyhow, time to fly away for the evening – see you soon!


1University of Oldenburg, Department of Biology and Environmental Sciences, Animal Navigation website, visited July 21, 2011.

2See, e.g., Heyers, D., Zapka, M., Hoffmeister, M., Wild, J., & Mouritsen, H. (2010). Magnetic field changes activate the trigeminal brainstem complex in a migratory bird Proceedings of the National Academy of Sciences, 107 (20), 9394-9399 DOI: 10.1073/pnas.0907068107, and Heyers, D., Manns, M., Luksch, H., Güntürkün, O., & Mouritsen, H. (2007). A Visual Pathway Links Brain Structures Active during Magnetic Compass Orientation in Migratory Birds PLoS ONE, 2 (9) DOI: 10.1371/journal.pone.0000937.

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