Looking for Help

4672605862_659b404a08_nMany dog owners would agree that there are few things more tragic to a playing dog than the ball rolling under the couch. Whenever it happened to my dog when I was in the room, she would look up at me, then back to the ball in what seemed like a silent plea for assistance. Of course, appearances can be deceiving. Some scientists argue that this human-directed gaze behavior, rather than being a form of intentional communication, is a learned response to certain situations: Based on previous experience, the dog has learned that when a desired object is out of reach, looking at a human leads to that object being moved within reach.

Marshall-Pescini et al. (2013) investigated this issue by giving dogs a task that, though first possible, became impossible in a later trial. They wanted to see if and how the dogs’ human-directed gazing behavior changed when the task became impossible. The task was to obtain food that was placed under an overturned, transparent Tupperware container. The food and container were placed on a board, so the food could be obtained using various strategies (e.g. turning the container over, pushing the container off the board). The first three trials were solvable, as the container was merely placed over the food. However, in the fourth trial, the container was attached to the board, making the task unsolvable. During all the trials, the dog’s owner (the “caregiver”) stood about a foot away from the board, facing it, while an experimenter also stood about a foot away from the board, adjacent to the owner.

Merely comparing the dogs’ behavior in the solvable and unsolvable trials would not rule out the theory that their human-directed gaze behavior is a learned response, so Marshall-Pescini et al. added a second condition. In the first condition (Attentive), both the owner and experimenter faced the board. In the second condition (Back), the owner faced the board, but the experimenter faced away from the board. If dogs’ human-directed gazes are a form of intentional communication, then presumably the dogs would gaze more at the person actually looking at them and the container. (This, of course, requires the dogs to understand that communication requires attention, or, at the very least, eye contact.)

Marshall-Pescini et al. also conducted this study with very young, preverbal children (15-27 months old), so they could directly compare dogs to humans. In this part of the study, the caregiver was the children’s nursery school teacher.

6872677550_318f2e60f0_nMarshall-Pescini et al. found that, in the unsolvable trials, both the dogs and the toddlers increased alternating their gaze between the caregiver and the container, compared to the solvable trials. Additionally, in the Back condition, they gazed more at the caregiver (who was facing the board) than at the experimenter (who was facing away from the board).

These results suggest that the human-directed gaze behavior of dogs (and toddlers) really is a form of intentional communication, rather than a learned response. We’ve already seen that dogs can understand human communication, but it seems that dogs can intentionally communicate with us, too!

(Although the overall results were the same, there were a few interesting differences in gazing behavior between the dogs and toddlers. For example, in the Attentive condition, dogs looked at both the experimenter and the caregiver for help, but toddlers looked at the experimenter much more than the caregiver. Marshall-Pescini et al. attribute this difference to some important discrepancies in environmental factors when testing the toddlers and dogs. First, the dogs were tested in a completely unfamiliar room, whereas the toddlers were tested in a room at their nursery school. Second, the “caregiver” in the dog experiment was the dog’s owner, while it was a nursery school teacher in the toddler experiment. How might these factors have caused the differences in gazing behaviors of the dogs and toddlers?)


Marshall-Pescini, S., et al. “Gaze alternation in dogs and toddlers in an unsolvable task: evidence of an audience effect.” Animal cognition (2013): 1-11.


This Little Piggy…

160px-Cute_PigletIn my very first post, I talked about how dogs can understand human social cues such as pointing to find hidden food. An interesting study published this month investigates whether domesticated pigs can understand human social cues, too.

The leading hypothesis of how dogs gained the ability to understand human social cues suggests that the ability may develop along with domestication (which I discussed here). It therefore seems reasonable that domesticated pigs may also possess the ability to understand human social cues.

Nawroth et al. (2013) conducted the study investigating the ability of young domesticated pigs to understand human social cues. Something I particularly like about this study is that they really tested the limitations of this ability in pigs by examining many factors, including the distance of the experimenter to the food and the length of time the experimenter pointed to the food.

The researchers used the same task throughout their entire experiment: an experimenter positioned between two bowls (only one of which contains food) makes some sort of cue towards the baited bowl, and then the pig chooses a bowl.

The first part of the study investigated two factors using what’s called a 2 x 2 factorial design. This type of study looks at two factors (independent variables), where each factor has two levels (a 2 x 2 x 2 factorial design would look at three factors with 2 levels each; a 3 x 3 factorial design would look at two factors with 3 levels each).

1519121063_0f075b7265_mThe first factor was the position of the experimenter: kneeling or standing. The second factor was the length of time the experimenter pointed to the food: one second (momentary) or until the pig chose a bowl (sustained). In a 2 x 2 factorial design, there will be four experimental conditions comprising all possible combinations of the factors; in this case, the conditions were: standing with momentary pointing, standing with sustained pointing, kneeling with momentary pointing, and kneeling with sustained pointing. The benefit to using a factorial design study is that it makes it easy to compare the effects of different factors (and combinations of factors) on the results (in this case, the pigs’ performance).

Nawroth et al. found that the pigs performed better than chance when the experimenter was kneeling, regardless of how long the experimenter pointed at the baited bowl. When the experimenter stood, however, performance was no better than chance. The researchers suggested two reasons why the pigs understood the kneeling experimenter better than the standing experimenter: one, the experimenter’s pointing hand was closer to the food in the kneeling condition than in the standing condition, so the pigs could rely on a close proximity between the experimenter’s hand and the bowl to make their choice. Alternatively, since pigs spend much of their time with their heads close to the ground, foraging, the standing experimenter may be outside the pigs’ field of attention (the pigs may not pay attention to things that far above the ground).

8076878857_2b39837f52_mTo investigate these two possibilities, Nawroth et al. tested the pigs on the two kneeling conditions from the first part of the experiment (momentary and sustained pointing), but this time, the bowls were farther apart from each other. Thus, in this part of the study, the distance between the kneeling experimenter’s pointing hand and the bowl was the same as the distance between the standing experimenter’s pointing hand and the bowl in the first part of the study.

The pigs performed above chance in both conditions, indicating that the height at which the social cue was presented, and not necessarily the distance between the experimenter’s hand and the bowl, affected the pigs’ performance.

Nawroth et al. further investigated the effect of the experimenter’s proximity to a bowl by testing the pigs with the experimenter either kneeling behind the baited bowl, or kneeling behind the empty bowl and pointing to the other (baited) bowl. They found that the pigs performed better than chance when the experimenter kneeled behind the baited bowl, but not when the experimenter kneeled behind the empty bowl and pointed to the baited bowl. So, while the pigs were unaffected by the distance between the experimenter’s pointing hand and the bowl in the second part of the experiment, the much closer distance between the experimenter and the bowl in this part of the experiment served as a strong cue for the pigs.

4902999050_85ab6bb35f_nNawroth et al. tested a few more factors with additional experiments – I don’t have space to detail them here, but you can read about them in the original paper, if you’re interested.

The gist of their study, though, is that pigs can understand human social cues including pointing (and also head and body orientation – part of the study I didn’t discuss here). There are some limitations to this ability (very close human proximity trumps the pointing gesture as a cue). But the fact that pigs are generally able to use these cues lends support to the hypothesis that this ability develops through domestication.

(As Nawroth et al. discuss in the introduction and discussion sections of their paper, the ability to understand pointing cues has also been found in other domesticated species, including cats, goats, and horses. However, none of these previous studies investigated head and body orientation cues.)


Nawroth, Christian, Mirjam Ebersbach, and Eberhard von Borell. “Juvenile domestic pigs (Sus scrofa domestica) use human-given cues in an object choice task.” Animal Cognition (2013): 1-13.

What’s in a Face?

3008056718_0162d2e2c4_mUndoubtedly the scariest time of year (besides maybe tax season) is Halloween – as October rolls around, we pause our perpetual avoidance of fear and instead embrace it, reveling in haunted houses and scary costumes. But how do we know what scary is, and why are many things universally frightening? Part of the answer could be cultural: for example, the mask from Scream or the hooded, scythe-wielding Grim Reaper. There could also be evolutionary influences on what we find frightening, such as sharp teeth and grotesque facial features.

Some scientists have approached this question from the field of face perception. They ask a more specific question: What makes a face scary? Previous research on face perception has examined the ability of humans (and, amazingly, some animals) to detect distorted faces, and has gauged preferences for attractive faces over unattractive ones. Sinnott et al. (2012) took this latter line of research further to investigate how animals and humans perceive scary faces – in particular, scary Halloween masks.

They began with three hypotheses about how non-human animals might react to the masks:

1. Human Cultural Hypothesis – Faces are scary not because of any particular way they look, but because of the cultural meaning associated with them. So a skull is scary because we associate it with death, the Scream face is scary because of its associations with the horror film, etc. If this hypothesis is true, we would expect animals to be unaffected by the masks, compared to humans.

2. General Biological Hypothesis – Many scary masks possess features commonly associated with predators, such as sharp teeth and large, angry eyes. This hypothesis predicts that animals would therefore perceive the masks as predators and be frightened of them.

3. Primate Biological Hypothesis – Primates have more complex faces than other animals – they can move facial features independently of each other to make various facial expressions, and they can use those expressions as way to communicate emotions like aggression and fear. Nonhuman primates thus may be more likely than other animals to perceive the frightening nature of the masks. If this is the case, then non-human primates, but not other animals, should be frightened of the masks.

In order to test these hypotheses, Sinnott et al. studied the avoidance response latency for animals to take food from a masked experimenter. In each trial, an experimenter wearing a mask offered an animal some food, then measured the amount of time the animal hesitated before taking it. If an animal is frightened, it will be more cautious and hesitate longer before taking the food. On the other hand, an animal unaffected by the mask will take the food with little or no hesitation.

Sinnott et al. tested 13 different Halloween masks, ranging from politicians to vampires to aliens. They also conducted control trials, where the experimenter was unmasked, to rule out the possibility that the animals were frightened by humans in general. They tested a wide variety of animals, including several primate species, lions, a bear, a camel, and macaws.

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The 13 masks used by Sinnott et al., plus a picture of the unmasked experimenter. (Source: Sinnott et al. 2012)

They found that primates had significantly longer response latencies than non-primates for all masks. There was no difference between primate and non-primate latencies in the control trials, ruling out the possibility that the primates were just more afraid of humans. Since only the primates were affected by the masks, Sinnott et al. rejected the General Biological Hypothesis, which posits that all animals should be frightened by the masks.

The fact that the non-human primates had longer response latencies suggests that the Human Cultural Hypothesis may also be incorrect, but Sinnott et al. wanted to directly compare non-human primates and humans by investigating whether they found the same masks to be scary. They asked humans to rate the masks on a scale of 1 (not scary) to 7 (very scary). When they compared those ratings to the non-human primates’ response latencies, they found a significant correlation – in general, non-human primates were more afraid of (had longer response latencies for) the masks that humans rated as scarier! This supports the Biological Hypothesis – the primates perceive the frightening nature of the masks, probably due to their greater sensitivity to facial expressions.


Example of a fear grimace

There were a couple interesting differences in how non-human primates and humans perceived the masks. For example, the non-human primates had longer response latencies for the politician masks, which the humans rated as not very scary. Sinnott et al. suggest that this is because the politician masks have big, toothy smiles, which the non-human primates likely perceive as “fear grimaces” (a smile-like baring of teeth that indicates fear).

The results of this study suggest that some higher-level cognitive process occurs in the primate brain when perceiving the scary masks (and probably faces in general). The presence of predator-like facial features (like big teeth) alone isn’t sufficient to elicit fear, or else all the animals would have been affected by the masks. Rather, primates may interpret what they perceive at a higher cognitive or even emotional level, which causes them to fear a face (or not).

So although humans may find some faces scary due to cultural associations, there’s also likely an evolutionary influence on the scariness of a face, based on facial features and their configuration, and requiring higher emotional and cognitive processes.

After all that talk about fear, I’ll end this post on a fun note: here’s a video showing how the animals at the London Zoo celebrated Halloween this year. Zoos often use holidays and birthdays as opportunities to provide the animals with themed enrichment (new and interesting things to explore and eat!).


Sinnott, Joan M., et al. “Perception of Scary Halloween Masks by Zoo Animals and Humans.” International Journal of Comparative Psychology 25 (2012): 83-96.