Interference at the encoding and maintenance of visual information

Two experiments are reported that examine the Irrelevant Picture Effect in visual working memory. When pictures that are irrelevant to a recall task are presented concurrently with the to-be-recalled items, they have been shown to cause selective interference: when the items are encoded visually the pictures cause interference, yet they cause no interference when the items are encoded verbally. When line drawings of common objects are used as irrelevant pictures, the results have been contradictory. Logie (1986) has shown that they cause visually selective interference while Quinn and McConnell's (in press) results suggest that they have a generally disruptive effect. The experiments follow up the explanation of general disruption put forward by McConnell and Quinn (submitted ms) that a sequence of drawings of common objects attracts general executive resources even under conditions where they are designated as irrelevant. It is shown that line drawings presented during item encoding cause general interference while selective interference is caused when the drawings are presented after the items have been encoded. The results are interpreted as showing that the recognition of a sequence of line drawings and the encoding of list items both require access to executive resources. Once the items have been encoded executive resources are no longer required and only the visual nature of the line drawings causes interference. The consequence of this type of interference is selective.