VENTRAL-STREAM FEEDBACK TO THE PRIMATE PRIMARY VISUAL CORTEX IS FOCUSED ON THE CENTRAL VISUAL FIELD: ANATOMICAL DATA IN SUPPORT OF A THEORETICAL PREDICTION

The central-peripheral dichotomy (CPD) theory is motivated by an attentional bottleneck that allows only a tiny fraction of visual inputs to reach recognition. It proposes that the peripheral visual field serves primarily to select this fraction, by directing gaze or attention, whereas the central field is specialised for recognising objects in the selected inputs. Accordingly, the theory hypothesizes that top-down feedback to aid recognition is strongest to the central visual field. Predictions on behaviour have been experimentally confirmed, including illusions that occur in peripheral but not central visual field, but whether anatomical feedback is really focused on central representations remains untested. To address this we injected cellular-resolution retrograde tracers in 12 sites of area V1 in marmoset monkeys. For each injection we quantified the neurons forming feedforward (FF) projections from the lateral geniculate nucleus, versus feedback (FB) projections from the extrastriate cortex. We found that the ratio of labeled FB to FF neurons decreased markedly with increasing eccentricity of the injection site. This decrease approximately followed a power law, and encompassed an order of magnitude across the range from 2˚ to 18˚ (Figure 1). The change in FB/FF ratio from ventral stream areas was more marked than that from dorsal stream areas. This is consistent with the CPD theory, as the ventral stream is more specialised for recognition processing. Beyond providing anatomical support for key predictions of the CPD theory, these results challenge the view of each cortical area as an anatomically uniform processing module, by demonstrating heterogeneity within V1.