Justin P. Halberda
Assistant Professor
Dept of Psychological & Brain Sciences
231 Ames Hall
3400 North Charles Street
Johns Hopkins University
Baltimore, MD 21218


phone: 410-516-6289
fax: 410-516-4478

Lab Sites

johns hopkins univ


Halberda, J., Sires, S.F., & Feigenson, L. (2006). Multiple spatially-overlapping sets can be enumerated in parallel. Psychological Science, 17 (7), 572-576.

Download the paper

-General notes on these demos: You will see a series of images of colored dots. Your task is to ignore the masks and report the number of dots in the set that is probed on each trial as best you can. The probe randomly appears either before or after the masks on each trial.

Experiment 1

Superset Trials

When adults were asked to enumerate the superset of all dots they succeeded on both probe-before and probe-after trials suggesting that they always encoded the superset of all dots irrespective of the number of colors.
  3-Color Probe-Before   5-Color Probe-After

Color Subset Trials

On 1-Color trials, adults succeeded on both probe-before and probe-after trials demonstrating that this task contacts the Approximate Number System.
  1-Color Probe-Before   1-Color Probe-After

On 2-Color trials, most adults succeeded on both probe-before and probe after trials.
  2-Color Probe-Before   2-Color Probe-After

With arrays containing 3 or more colors, adults succeeded on probe-before trials but showed increased error on probe after trials (adults underestimated the number of dots in the probed set or failed to encode it). This limit of three sets suggests that participants could store each set as an individual in a single slot in visual short-term memory with numerosity stored as a feature of each set.
  4-Color Probe-Before   6-Color Probe-After

6 trials, one after the other, to give you a sense of what it feels like to do this task.
Note: In the actual experiment, response screens remained on until the participant pressed ‘return’ after typing their answer. RT and accuracy were measured.

  Exp1, 6 Trials

Experiments 2 & 3

These experiments were similar to Exp 1, but the stimuli were controlled for total area (Exp 2) and circumference (Exp 3). As in Exp 1, adult, on average, encoded 3 sets in parallel. This suggests that responses were based on numerosity and not on some other visual feature correlated with numerosity.
  Exp2, 4-Color Probe-Before   Exp2, 5-Color Probe-After
  Exp3, 5-Color Probe-Before   Exp3, 6-Color Probe-After