Macaque monkeys experience visual crowding

Abstract

In peripheral vision, objects that are easily discriminated on their own become less discriminable in the presence of surrounding clutter. This phenomenon is known as crowding.The neural mechanisms underlying crowding are not well understood. Better insight might come from single-neuron recording in nonhuman primates, provided they exhibit crowding; however, previous demonstrations of crowding have been confined to humans. In the present study, we set out to determine whether crowding occurs in rhesus macaque monkeys. We found that animals trained to identify a target letter among flankers displayed three hallmarks of crowding as established in humans. First, at a given eccentricity, increasing the spacing between the target and the flankers improved recognition accuracy. Second, the critical spacing, defined as the minimal spacing at which target discrimination was reliable, was proportional to eccentricity. Third, the critical spacing was largely unaffected by object size. We conclude that monkeys, like humans, experience crowding. These findings open the door to studies of crowding at the neuronal level in the monkey visual system.

Spatial contextual effects in primary visual cortex limit feature representation under crowding

“…We conclude that both humans and macaque monkeys exhibit crowding for our displays (see ref. 34 , for a similar comparison for displays of letters). Crowding was manifest as an elevation of discrimination threshold, which varied from roughly 25% to 70% depending on the subject and precise details of the visual display.…”

Behavioral read out of population value signals in primate orbitofrontal cortex

“…The reason is that in each trial the two choice targets were obscured from view until the monkeys fixated upon them directly, an effect achieved through the use of visual crowding (Fig. 1c) 28,29 and a dynamic display that was contingent upon gaze (see Methods, and also Hunt et al 21 for a similar approach). The monkeys therefore viewed the targets sequentially, by fixating them one at a time.…”

“…1c). Crowders reduce the effectiveness of peripheral vision 28,29 , making it difficult to identify a target without using high-acuity foveal vision. Second, we used gaze-contingent programming to initially obscure the targets until the first eye movement was made: At the moment the target arrays first appeared on the display, the two targets were masked with a randomly generated crowder (Fig.…”

What crowds in crowding?

“…One main reason is that objects, as letters, are rarely met in isolation in normal life. Thus, crowding is the predominant situation for object recognition for humans and animals, and indeed, the characteristics of crowding are similar in humans and monkeys (Crowder & Olson, 2015).…”