Abstract
Pigeons learned to discriminate two different patterns displayed with miniature light-emitting diode arrays. They were then tested with 84 interspersed, non-reinforced degraded pattern pairs. Choices ranged between 100% and 50% for one or other of the patterns. Stimuli consisting of few pixels yielded low choice scores whereas those consisting of many pixels yielded a broad range of scores. Those patterns with a high number of pixels coinciding with those of the rewarded training stimulus were preferred and those with a high number of pixels coinciding with the non-rewarded training pattern were avoided; a discrimination index based on this correlated 0.74 with the pattern choices. Pixels common to both training patterns had a minimal influence. A pixel-by-pixel analysis revealed that eight pixels of one pattern and six pixels of the other pattern played a prominent role in the pigeons’ choices. These pixels were disposed in four and two clusters of neighbouring locations. A summary index calculated on this basis still only yielded a weak 0.73 correlation. The individual pigeons’ data furthermore showed that these clusters were a mere averaging mirage. The pigeons’ performance depends on deep learning in a midbrain-based multimillion synapse neuronal network. Pixelated visual patterns should be helpful when simulating perception of patterns with artificial networks.
Highlights
With so many laboratory pigeons in the contemporary behavioural literature responding to complex images on touchscreens, the fact that their wild ancestors’ pecking behaviour mainly evolved as a plain manoeuvre to acquire food has almost been forgotten
Through these grooves the experimenters could simultaneously push forward two white pinewood strips, 2.5 cm wide, 0.3 cm thick, 10 cm long, so that they both protruded 2.5 cm into the cage. This brought two fields of 15 × 15 mm, each with a set of 3 × 3 punch-stamped hemispherical depressions at the ends of the strips into the pigeons’ view and access. These two fields were each filled with five brown milo seeds (Sorghum bicolor) snugly occupying the two nine-hollow fields according to patterns resembling a z or a + (Fig. 1)
The + pattern consisted of five milo seeds firmly but invisibly glued to the wooden strip with a small drop of epoxy adhesive, whilst the five milo seeds of the z pattern would always lie loose in the hollows; for the other two pigeons the arrangement was the precise converse
Summary
With so many laboratory pigeons in the contemporary behavioural literature responding to complex images on touchscreens, the fact that their wild ancestors’ pecking behaviour mainly evolved as a plain manoeuvre to acquire food has almost been forgotten. The pigeons were prevented from seeing the experimenter by a vertical white-clad hardboard screen with a rectangular 6 × 12 cm port covered with grey nylon gauze serving as a one-way window Through it one could view the brightly illuminated milo-seed fields and record the first peck-grasp response of the pigeons towards the two different food offerings. Pigeons customarily peck grains out of a small pattern, or a small heap, at the rate of about 3 pecks per second[9,10,11] For adequate resolution, their seed (and grit) choice behaviour has to be high-speed video recorded and slow-speed reviewed, a procedure that unless automated, is too time- and labour-consuming for routine use. Our laboratory regularly employed a derived but much simplified grit–grain discrimination procedure to assess the visual competences of pigeons in various contexts[12,13,14] (see [15], for related experiments on neonate chickens)
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