integration by alicejenny

VIEWS: 6 PAGES: 119

									              Masking occurs when
 the perception of a brief stimulus (the target)
   is impaired by another stimulus (the mask)
presented in close temporal and spatial contiguity


              Why study masking?
  Because it opens a window on the mind/brain


    Masking occurs in two main flavours:
           a) by integration (camouflage)
           b) by interruption:
                     i) metacontrast masking
                    ii) pattern masking
                   iii) object-substitution masking

          Let’s start with integration…
            Masking by temporal integration


                                CW:
            Masking by temporal integration is mediated
                       by visible persistence
                           (iconic memory)



Visible Persistence: an image that remains visible for a brief
                        period after the display has been turned off.
                        (NOT a retinal afterimage)
Storage model of visible persistence
        (hydrodynamic metaphor)


                                  Sensory store
Storage model of visible persistence
  (the metaphor can also be electrodynamic)




 sensory store             visible persistence




                                    time

            (10 ms)
 How can we measure the duration of visible persistence?




                Task: name the matrix location of missing dot




Present the matrix in two sequential frames, separated by an ISI




                              ISI


                   F1                     F2
          Short ISI




          F1   ISI   F2
           time




F1   F2                   time
     Long ISI



         ISI
F1                          F2
     time

        No overlap



      No integration




F1                     F2   time
                            F1      ISI   F2
                                                                 time


     F1                           ISI     F2


F1                          ISI           F2

                            100
                                                           VDL
                             80
          Percent correct




                                                           JH
                                                           BJ
                                                           DR
                             60

                             40

                             20

                              0
                                    40    80     120 160   200
                                                                        mat1 noarg space
                                               ISI (ms)
Charging the sensory store (increasing the duration of F1)


                                 F1      ISI        F2
                                                                    time


                   F1                    ISI        F2




     F1                                  ISI        F2



                      100
                                                              VDL
                            80                                RGB
          Percent correct




                                                              SKP

                            60

                            40

                            20

                            0
                                 10 40         80   120   160 200
                                      Duration of F1 (ms)                  mat1 noarg space
F1 duration = 16 ms
      F1 F2




F1 duration = 300 ms
      F1               F2




     (ISI = 0)




                            mat1 noarg space
      When F1 is long, integration breaks down.
          F1 and F2 become segregated




In fact, when F1 is long, F1 and F2 become segregated
          even when displayed concurrently




                                   F2
                       F1




                                                  Demo: mat2 20-1-0
      Visible persistence is time-locked
to the onset of the stimulus, not to its offset



 This means that temporal integration follows
         an SOA law, not an ISI law



               This also means
           that visible persistence
  is not based on a decaying sensory store.
Visible persistence is linked to a burst of neural activity
              time-locked to stimulus onset
                 (Duysens, Orban, & Maes, 1985)   .
                      In brief,
The duration of visible persistence varies inversely
              with stimulus duration
             (inverse-duration effect)




                                              time
                         F1   F2




                    F1        F2




               F1             F2
                     All these effects
(integration at short SOAs and segregation at long SOAs)
                      can be explained
   based on ideas of von Holst (1954) and MacKay (1957)



    The onset of a stimulus creates an image of itself
                  (opens an object file)
      that accepts new data for a very brief period
           (the critical period of integration)


    After that, the image acts as a filter that passes
                     only new stimuli
Short SOA:

  F1   F2


             The critical period is up:
             the object is complete.
             No more parts can be
             added.
Long SOA with ISI:

       ISI
 F1                 F2


             The critical period is up:
             the object is complete.
             No more parts can be
             added.
Long SOA, no ISI:
                    F2

                    F1
Applying the principles of temporal integration
        to forward masking by pattern



    mask                            target
Masking by temporal integration



      mask            target




             msk    tgt
             time




                                  Demo: int1-4
In the matrix task a long F1 produced segregation.
     A long leading mask produces unmasking.


                                       tgt
                      mask

                      time


mask                                mask + target




                                                     Demo
       tgt
mask

time




             seg1-4
         msk                tgt




DURATION OF LEADING MASK (ms)
                      tgt
           msk




DURATION OF LEADING MASK (ms)
An account based on ideas of von Holst (1954) and MacKay (1957)
     (Long SOA)
                     tgt
          mask




      mask msk+tgt
       On the basis of this evidence, one might conclude that forward masking never
          occurs when the leading mask is displayed for longer than about 100 ms


But note the effect of task switching (e.g. conventional display sequence in masked priming)
                                                        No
                    Stream                            stream                                                  440

                            5                              5                                                  420
                        C                              C




                                                                                         Reaction Time (ms)
                    7                                                                                         400
                                                     440
                5                                                                                             380
                                                     420
            9

                                Reaction Time (ms)
                                                     400
        2                                                                                                     360
                                                     380
    3
7
                                                     360                                                      340
                                                     340

                                                     320
                                                                                                              320
                                                     300
                                                               Grid Noise Digit Script
                                                                                                              300
                                                           Leading Distractors
                                                                                                                      No Stream
                                                                                                                    Stream

                No forward masking in either case when no backward mask is presented


                RT differences mediate more backward masking in the Stream condition
Masking occurs in two main flavours:
       a) integration (camouflage)
       b) interruption:
              i) metacontrast masking
             ii) pattern masking
            iii) object-substitution masking
                   Metacontrast masking

No spatial overlap between target and mask

When target-mask SOA is short, the target’s visibility is reduced
(but not when SOA is equal to zero)
Conventional demonstration of metacontrast masking
                  (visibility ratings)



                     TARGET
Conventional demonstration of metacontrast masking
                  (visibility ratings)



                       MASK
           SOA = 0
          No masking


(10 ms)




(10 ms)
   Stimulus sequence
in metacontrast masking




      SOA
    Visibility ratings are subjective



Target           Mask         Target + Mask
          SOA = 0
         No masking


         (10 ms)
Target


         (10 ms)
Mask
sim
sim
sim
sim
            Stimulus sequence
         in metacontrast masking

                     ISI


Target
                    SOA



Mask
seq
seq
seq
seq
U-shaped curve
                                               SOA

                                        tgt               msk




                   100
                 100
              % correct responses
ondition
tch. Gap                     80
                            80
     varied
ed     10                    60
                            60
ed    100
                             40
                            40                                  Average
       10
                                                                   Br. Mtch.
                                                                  No ISI
0     100                   20
                             20                                   With ISI
                                                                  Gap
                                    0   40           80     120       160
                                              SOA (ms)
Effect of varying the SOA
SOA = 0
SOA = 100
SOA = 200
SOA = 300
SOA = 500
      Effect of
target-mask separation
    (SOA = 100 ms)
Sep = 1
Sep = 2
Sep = 3
Sep = 4
Sep = 5
Reducing the mask’s contours
      (SOA = 100 ms)
4 dot 1
4 dot 2
4 dot 3
4 dot 4
                                    Function of SOA, not ISI (SOA law)

                                          With ISI               ISI
                                                      tgt                msk

                                          No ISI            tgt          msk


                   100
                 100
              % correct responses
ondition
tch. Gap                     80
                            80
     varied
ed     10                    60
                            60
ed    100
                             40
                            40                                         Average
       10
                                                                          Br. Mtch.
                                                                         No ISI
0     100                   20
                             20                                          With ISI
                                                                         Gap
                                      0         40          80         120     160
                                                     SOA (ms)

                                     NOTE: no masking when SOA = 0
A theory of metacontrast masking:

    Cross-Channel Inhibition

(Breitmeyer & Ganz, 1976, 2005)
1.   A brief display generates activity in two visual channels:
     a) Transient channels (short latency; short duration; low SF; mediate perception of stimulus onset)
     b) Sustained channels (long latency; long duration; high SF; mediate perception of stimulus identity)

2.   Activity in the transient channels suppresses activity in the sustained channels




                                       no masking when SOA = 0




                                                                                  time


          target
                                   +                +


           mask
1.   A brief display generates activity in two visual channels:
     a) Transient channels (short latency; short duration; mediate perception of stimulus onset)
     b) Sustained channels (long latency; long duration; mediate perception of stimulus identity)

2.   Activity in the transient channels suppresses activity in the sustained channels




                                                                             time


     target




      mask
Support for the cross-channel inhibition hypothesis

        inhibition vanishes in scotopic viewing (von Békésy)
                 and so does metacontrast masking



    Light-adapted                                    Dark-adapted
Masking of a pattern by parts of itself reveals a new form of masking:
                         Object substitution


                            F1          F2




                          (30 ms)    (300 ms)




     F2                                                      F2




                                                              Demo:
      F1                                                      mat2 0-2-0
                                                              mat2 0-2-20
                                                              (vary overlap)
This is unquestionably a form of masking but:


The mask consists of a portion of the target
The target-”mask” SOA is equal to zero


  Remember: no metacontrast masking when SOA = 0

  So, let’s turn this into a classical metacontrast paradigm,
  and see if masking occurs when SOA = 0
Metacontrast paradigm


  target          mask




           time


      SOA = 0
demo




       0
1x
2x
3x
4x
The finding that metacontrast masking occurs when T-M SOA = 0
              is inconsistent with accounts based on
                   inhibitory contour interactions




     +     +
                In addition,
          common-onset masking
occurs without substantial masking contours

               (four-dot masking)
1dotx
2dotx
3dotx
4dotx
Common-onset masking occurs with overlearned geometrical shapes
The target can be seen easily when the
  entire display is presented briefly




           (10 ms)
os16-0a
os16-0b
os16-0c
os16-0d
   Display sequence for
object-substitution masking



        (10 ms)




                  (320 ms)
os16-600a
os16-600b
os16-600c
os16-600d
How does object substitution
       come about?
?
Object-substitution masking does not occur when set size = 1




                         (10 ms)


                                   (320 ms)
os1-600a
os1-600b
os1-600c
os1-600d
  Object substitution masking does not occur
when attention is directed to the target location
X




    os16-600a
X




    os16-600b
Expectation based on learned regularities
(occlusion of far objects by near objects)
              influences OSM
         Kahan & Lichtman (P&P, in press)




                                   30 ms




                                            600 ms
Expectation based on learned regularities
(occlusion of far objects by near objects)
              influences OSM
         Kahan & Lichtman (P&P, in press)




                     far
                                                                   near
          % C (common - delayed offset)




                                          10
                                          8
                 Masking Effect




                                          6
                                          4
                                          2
                                          0
                                               n-n f-f f-n n-f
                                          -2   Target-mask depth
                 Common-onset masking has two components



Inhibitory contour interactions
      early
      photopic
      independent of attention
      requires substantial masking contours
      does not occur at SOA = 0




Object-substitution                                  ?
      relatively late
      scotopic
      critically dependent on attention
      requires minimal masking contours
      occurs at SOA = 0
Separating the two components of common-onset masking:
                     (inhibitory contour interactions and object substitution)




                                     Photopic                        Scotopic

                       100                           100
      % correct responses




                            80                        80


                            60                         60

                                                        Set Size
                                                      (No. elements)
                            40                                   1
                                                                 2
                                                                 4
                                                                 8
                            20                                  16

                                 0   80 160 240 320         0    80 160 240 320
                                                Duration of mask (ms)
Separating the two components of common-onset masking:
        (inhibitory contour interactions and object substitution)



                                       photopic
                                       scotopic
Masking occurs in two main flavours:
       a) integration (camouflage)
       b) interruption:
              i) metacontrast masking
             ii) pattern masking
            iii) object-substitution masking
Pattern masking is probably the most commonly used form of masking
            but, in my opinion, it is the least interesting



      Depending on viewing conditions, it includes aspects of both
                 integration and object substitution
Here is one way in which the processes of integration and interruption
          (object substitution) may combine to yield masking
                        (Michaels & Turvey, 1979)
Ciao!

								
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