October 24, 2016

Pigeons spot cancer as well as human experts

Representational Image

They may have a reputation for being bird-brained, but pigeons have found to be as adept as humans when it comes to spotting cancerous tissue in mammograms.

Experts trained a group of the birds to tell the difference between benign and malignant human breast tissue using food reinforcement techniques.

Over the course of two weeks, the birds’ accuracy at studying the slides improved from 50 per cent up to 85 per cent – and in one instance this rose as high as 90 per cent.

For the study, each pigeon learned to discriminate cancerous from non-cancerous images and slides using traditional ‘operant conditioning’.

This involves only rewarding the bird when a correct selection was made.

If they made an incorrect selection they received no treat and continued until they got the right result.

The training used stained pathology slides, including a large set of benign and cancerous samples from routine cases at UC Davis Medical Centre.

Some birds first learned to recognise benign or malignant samples in full colour at low magnification (4X) and then progressed to medium (10X) and high (20X) magnifications.

They were also tested using monochrome samples to eliminate colour and brightness as potential cues, as well as samples with different levels of image compression – a procedure commonly used to reduce the size of digital data sets.

To rule out the possibility that the birds memorised the test, brand new samples were presented and food was dispensed regardless of whether the pigeons made a correct selection.

The pigeons performed virtually as well on images that they had never been shown before.

Like humans, the birds’ accuracy was slightly affected by the presence or absence of colour in the images, as well as their quality.

The birds also learned to correctly identify micro-calcifications, which are small accumulations of calcium salts in the tissue, they struggled to classify suspicious masses on mammograms – a task considered difficult even for medical specialists.

Their accuracy averaged 84 per cent for images with microcalcifications that they had been trained upon, and 72 per cent for new images – a level of performance on par with human radiologists who were given the same cases to review.

The birds, however, had difficulty evaluating the malignant potential of breast masses detected on mammograms according to the study published in the journal Plos One, a task which the authors describe as ‘very challenging.’

Human radiologists achieved an accuracy rate of about 80 per cent when viewing images of the relatively subtle masses used in this study.

But, the pigeons took many weeks, instead of days, to ‘master’ the histopathology tasks and learn to classify the breast masses in the mammogram training set.

‘These results go a long way toward establishing a profound link between humans and our animal kin,’ said study co-author Edward Wasserman, professor of psychological and brain sciences at the University of Iowa.

‘Even distant relatives – like people and pigeons – are adept at perceiving and categorising the complex visual patterns that are presented in pathology and radiology images, surely a task for which nature has not specifically prepared us.’

The pigeons’ successes and difficulties could also shed light into how physicians process visual cues on slides and X-rays to diagnose the potentially deadly disease.

Elsewhere, using the birds’ remarkable ability to discriminate between complex visual images could help researchers explore the importance of colour, brightness and compression on the experts’ ability to spot cancers.

These findings are particularly surprising since a pigeon’s brain is no bigger than the tip of an index finger, although the neural pathways involved operate in ways similar to the human brain.

Professor Wasserman said the common pigeon has a tremendous capacity to discriminate and categorise a wide range of objects and images.

‘Research over the past 50 years has shown that pigeons can distinguish identities and emotional expressions on human faces, letters of the alphabet, misshapen pharmaceutical capsules, and even paintings by Monet vs Picasso,’ Professor Wasserman said.

‘Their visual memory is equally impressive, with a proven recall of more than 1,800 images.’

It was co-author and University of California Davis researcher Richard Levenson’s idea to investigate whether pigeons could ‘read’ mammograms, building Professor Wasserman’s earlier research on visual short-term memory capacity of pigeons and people.

Dr Levenson, professor of pathology and laboratory medicine at UC Davis Health System said: ‘The birds were remarkably adept at discriminating between benign and malignant breast cancer slides at all magnifications, a task that can perplex inexperienced human observers, who typically require considerable training to attain mastery.

‘Pigeons’ accuracy from day one of training at low magnification increased from 50 per cent correct to nearly 85 percent correct at days 13 to 15.’

Professor Wasserman, who has conducted studies on pigeons for more than 40 years, found the pigeons are especially adept at discerning pathology slides.

‘The pigeons learned to discriminate benign from cancerous slides as fast in this research as in any other study we’ve conducted on pigeons in our laboratory,’ he said.

‘In fact, when we showed a cohort of four birds a set of uncompressed images, an approach known as “flock-sourcing,” the group’s accuracy level reached an amazing 99 per cent correct, higher than that achieved by any of the four individual birds.’

After the training phase, however, when the birds were finally shown previously unseen images they failed to perform at a level better than chance.

‘The data suggest that the birds were just memorising the masses in the training set, and never learned how to key in on stellate margins and other features of the lesions that can correlate with malignancy,’ Professor Levenson said.

‘But, as this task reflects the difficulty even humans have, it indicates how pigeons may be faithful mimics of the strengths and weaknesses of humans in viewing medical images.’

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