Memory formation of object representation :natural scenes
Eiichi Hoshino12 , Fumihiko Taya2 , and Ken Mogi12
1

Tokyo Institute of Technology, eiichi@brn.dis.titech.ac.jp
2Sony Computer Science Laboratories

Abstract. It has been suggested that the parahippocampal region collects spatial information in relation to navigational objects, in a joint
encoding of space (Janzen and van Turennout (2004)). The navigational
object may play a role of ”landmark” when the episodically dispersed
snapshots are combined into comprehensive spatial information of an individual space. Here we study the nature of object recognition in the longterm memory in human cognition that is learnt during scene-integration
as regards the viewing angle under attention control. Based on the result, it is suggested that objects in a scene without attention may beprocessed into a 2-D representation bound to the background scene as atexture.

1

Introduction

The interpretation of spatial relationships is an important factor in contextual
behaviours and the formation of episodic memory. The classic key idea of spatial
information processing has been analysed by O’Keefe and Nadel [1]. Together
with discovery of ”place cells” and concept of ”cognitive map” [2], they proposed the cognitive map theory in which place cells, dead reckoning system
and landmark navigation are combined into allocentric map-based navigation in
hippocampus formation. On the other hand, Yamaguchi et al. have proposeda mechanism of hippocampal memory encoding of episodic events from novel
temporal inputs caused by theta phase precession [3]. More recently, Janzen andvan Turennout demonstrated that the parahippocampal region collects spatial
information in relation to various objects, in a joint encoding of space and objects [4]. To produce allocentric long-term memory (LTM), it is necessary thatthe egocentric representations primarily obtained from perceptual information
are combined together. In a case of absence of self motion, the production ofallocentric LTM crucially relies on the integration of diﬀerent scenes. If scenes
are episodically dispersed, it is required that there be navigational landmarks inthe scenes to combine these scenes into coherent allocentric representations.
Current study focuses on the observation of object recognition underlying
human cognition after episodically dispersed views are combined into comprehensive spatial information of an individual space. Additionally, attention enhances the visual LTM (VLTM) of previously attended objects embedded in anatural scene [5], which is supported by a dynamic evolution model on attention
and memory [6], suggesting that object representations in LTM may also be
aﬀected by attention. Thus, we also study the eﬀect of attention on the object
representations revealed in a later recognition task.

2ExperimentsTo investigate the nature of object representations within human cognition in
LTM that is learnt during scene-integration, experiment 1 was designed especially as regards the viewing angle with attention control, in the context ofintegration of the spatial information. In the leaning phase, participants were,in turn, viewed two dispersed views in which the several objects were located.
They were instructed to remember objects on green bases and their position
while those on blue bases were distractors at the moment. After the learning
phase, they were required to conduct a two-alternative forced-choice recognition
test. The objects presented in the test phase were divided into three types; i.e.
objects viewed from same angle as the learning phase, those from diﬀerent angles
and novel objects. The objects were chosen from everyday use objects in same
basic-level category (i.e. chairs, in this study) to make the diﬀerent visual angle
recognition easy because the aim of the experiment is to study the nature of object representations in LTM, but not in short-term memory (STM) in which themulti-angle object representations would be more easily established than thosein LTM. Consequently, experiment 2 was carried out as the same as experiment
1 but the background in learning phase were changed to monochromatic.
2.1

Results

The rate of correct judgement (RCJ) (familiar or new) was signiﬁcantly higher
for the attended objects (green bases) compared to the unattended objects (bluebases). A 2 by 2 repeated-measures analysis of variance (ANOVA) (attention byvisual angle) on the RCJ showed a signiﬁcant eﬀect of attention (F (1, 8) =7.977, P = 0.022 < 0.05), whereas no signiﬁcant eﬀect of visual angles andno interaction between same and diﬀerent visual angles (F (1, 8) = 0.397, P =0.546) (Fig. 1 (a)). The RCJ on unattended objects viewed from the same visual
angle was higher than that for rotated objects, although the diﬀerence was notstatistically signiﬁcant (Fig. 1 (a)). The RCJ on unattended objects viewed from
diﬀerent visual angle was signiﬁcantly lower than that on attended objects, (p <.05), while that on attended objects had no signiﬁcance. The RCJ on objects
located at a certain spatial conﬁguration, such as right- or left turn corner andcrossroads, was not consistent in conditions with any particular visual angles.
A few participants reported that remembering the objects and their location
was too diﬃcult and could not conﬁdentially discriminate familiar or new for
the most of the objects. However the tendency in less RCJ on the unattended
objects presented from diﬀerent visual angle was observed among participants.
A motivated participant showed that good performances in both types of RCJ

for attended objects, but again his RCJ for unattended objects viewed from
diﬀerent angles was signiﬁcantly poor.
In experiment 2, no statistically signiﬁcant diﬀerence was observed amongthe 4 conditions, although both types of RCJ of objects from diﬀerent visual
angles appeared to be higher than that of objects from same visual angles (Fig.
1(b)).
(a)Same visual angle
Diﬀerent visual angle

0.7

(b)

Same visual angle
Diﬀerent visual angle

0.7*0.60.6

0.5

0.5

0.4

0.4

0.3

0.3

0.2

0.2

0.1

0.1

0.0

0.0

Attended

Unattended

Attended

Unattended

Fig. 1. Rate of correct judgement (RCJ) for the objects in experiment 1 and 2. (a)RCJ for attended and unattended objects viewed from same and diﬀerent visual angles in experiment 1. (b)That in experiment 2. Error bars are standard errors acrossparticipants.

3Discussion

The result that overall VLTM of attended objects was relatively well establishedcompared with that of unattended objects is consistent with previous work by
Hollingworth [5], supporting that attention to objects in a scene enhanced theconsolidation of memory for navigational landmark representations. Moreover,
the accuracy on attended object recognitions from diﬀerent visual angles indicates the role of attention is producing the angle invariant object representations.
The inconsistency between the succeeded recognition for object from particular visual angles and the spatial conﬁgurations suggests that the memory ofobject representations do not include the spatial conﬁgurations around the object. (But see Hollingworth 2006 [8]). This supports Mallot and Gillner’s ﬁndingthat the local views and objects are recognised individually and not recognised
as conﬁgurations among objects when navigating in a large-scale environment[9]. The selective activation for navigational objects previously showed in a scene
but not for non-navigational objects, found by Janzen and van Turennout, inthe parahippocampal gyrus [4] may not support encoding of spatial conﬁgurations around the objects. The result that the RCJ vary according to attention
could predict that the nature of object representations would reﬂect only object
intrinsic representations, again consistent with Mallot and Gillner’s ﬁnding. TheVLTM of object representations is strongly bound to a presented scene [8]. If
attention plays a role in extracting focal information, a cognitive stage of object
representations may be produced by attention. Therefore, attention may support to obtain the view-invariant or 3-D representations of objects from a scene,
but in absence of attention, such representations are never obtained. Rather theobject-to-scene binding gives rise to a perception of objects as a texture in thescene. In this view, the failure of recognition in unattended and depth rotation
may arise from the object-to-scene binding.
Whereas unattended objects in a scene might be primarily treated as a texture bound to the scene in the VLTM without any 3-D structural information.
The failure to recognise rotated objects whose orientation is novel for subjects
may reﬂect the strong object-to-scene binding where an object is regarded as apart of plain surface of a scene, resulting in inhibition priming.

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