Visual orientational anisotropy and stimulus surround effects in discrimination of spatial numerosity. 
Visual spatial numerosity perception was investigated as a function of spatial orientation and surround conditions.  3 to 13 dots arranged linearly in horizontal, vertical, or oblique orientations were presented for 200 msec.  in either a square or circular stimulus field.  For patterns with small numbers of dots (3 to 7), surround and orientation conditions did not substantially alter perceived number except vertical arrangements were judged as having reliably more dots than identical horizontal arrangements.  For large dot-number patterns (8 to 13), surround significantly altered perceived number and left oblique linear arrangements were judged to have reliably more dots than equivalent arrangements in all other orientations.